Portugal secured a last-gasp 2-2 draw on Sunday with Silvestre Varela heading home in the final minute to deny the United States victory.
The USA had come from behind to lead 2-1 on Sunday and looked to have ended Portugal's FIFA World Cup campaign in Manaus, before Cristiano Ronalo got free on the right in the fifth minute of second-half stoppage time and picked out Varela, who powered a header past Tim Howard.
An early goal to Nani saw Portugal respond well to their devastating 4-0 loss to Germany last week, but second-half strikes to Jermaine Jones and captain Clint Dempsey had put the USA in front and on the verge of securing a berth in the round of 16 for the second tournament in a row.
But Varela's late header ensured the top two positions in Group G remain up for grabs with Germany (four points) on top, level with the USA, while Ghana and Portugal both have slim chances of advancing with one point each.
Despite speculation that a knee injury would keep him out of Portugal's line-up, Ronaldo started, while Helder Postiga, Ricardo Costa, Andre Almeida and Beto replaced the unavailable quartet of Hugo Almeida (thigh), Pepe (suspension), Fabio Coentrao (groin) and Rui Patricio (thigh).
Klinsmann picked Graham Zusi to replace the injured Jozy Altidore (hamstring) with the Sporting Kansas City midfielder lining up on the left and Dempsey moving into a lone striker's role.
The match started horribly for the USA with Nani opening the scoring in just the fifth minute.
Miguel Veloso's poor cross bounced in front of Geoff Cameron and the central defender sliced his clearance to the back post, where Nani took a touch and then smashed his shot high into the net with Howard stranded.
Portugal pinned the Americans back in the opening stages with Klinsmann's side creating their first decent opportunity when Fabian Johnson, who was a regular outlet pushing up from right-back, got free in the 10th minute but his shot was deflected for a corner.
Six minutes later, Portugal's injury curse seemingly struck again with Postiga getting subbed off for Eder with an apparent hamstring strain.
The substitution seemed to halt Portugal's momentum, with Michael Bradley and Dempsey each failing to convert a pair of half chances for the USA before the half-hour mark.
Portugal reminded the USA of their counter-attacking threat three minutes before half-time with Nani unleashing a scorching drive that was parried by Howard, while in the 45th minute, the American gloveman made a double save to ensure his team were just 1-0 behind at the break.
Although Howard was unimpressed by his initial save onto the post from a strike from Nani, the 35-year-old did brilliantly to keep his balance and tip Eder's follow-up over the bar.
Almeida came off at half-time with another possible injury, with Veloso moving to left-back and William Carvalho promoted to defensive midfield.
The second half almost started exactly as the first had with Eder acrobatically volleying over the bar after another poor clearance from Cameron, before Johnson got forward to force Beto into a save.
In the 55th minute, Bradley should have equalised when Johnson again got free on the right, cutting it back but the Toronto FC midfielder's shot was blocked on the line by Costa.
The USA notched a deserved equaliser in the 63rd minute when a corner was cleared to Jones and the Schalke midfielder smashed his shot inside the far post, while Howard made another sharp save soon after to deny Raul Meireles.
Although Portugal had a few chances to lead again, the USA hit the front with nine minutes remaining when Zusi collected a loose ball in box and crossed for Dempsey to score off his midriff, although Klinsmann's men were denied victory thanks to Varela's late heroics.
|13||J. Jones||64' 75'|
|Coach: J. Klinsmann|
for A. Bedoya 72'
for C. Dempsey 87'
for G. Zusi 90+1'
|Copa Libertadores success ´a dream´ for Borja|
|Pochettino honoured by Simeone comparisons|
|Argentina have not asked for Sampaoli - Monchi|
|Ancelotti: Fitness the key for Bayern|
|Bayern win ´a small foundation´ for Montella´s Milan|
|Icardi missing due to injury - Mancini|
|Emery satisfied with warm-up win over Madrid|
|Conte quiet on Tevez, apologises for Fabregas red|
|´It was far from a friendly´ - Klopp on Chelsea defeat|
|Madrid off the pace, concedes Zidane|
|Chelsea 1 Liverpool 0: Cahill´s header seals win|
|Grujic says Chelsea´s Matic told him to sign for Liverpool|
|Bolasie wants to see Berahino and Benteke at Crystal Palace|
|Rodgers hails ´outstanding result´ as Celtic draw|
|Walcott claims level of MLS is close to Premier League|
|Bayern Munich 3 AC Milan 3 (3-5 on penalties): Bonaventura seals win|
|Atletico Nacional 1 Independiente del Valle 0 (2-1 agg): Borja secures Copa Libertadores crown|
|Icardi absent again as Inter held by Estudiantes|
|Real Madrid 1 Paris Saint-Germain 3: Zidane oversees poor pre-season start|
|Hazard vows to rediscover best Chelsea form|
|Klopp reveals why he sent Sakho back to Liverpool|
|Tevez: Conte wanted me at Chelsea|
|Sunderland hopeful Defoe will be fit for Man City opener|
|Sundowns overcome Zamalek to book semi-final spot|
|Falcao scores as Monaco return ends in defeat to Fenerbahce|
|Southampton overcome Twente, Asoro stars for Sunderland|
|Man City must adapt to Guardiola tactics quickly - Denayer|
|Chelsea and Leicester to play in EFL Trophy as five Premier League clubs refuse|
|Tolisso pulls plug on €37.5m Napoli move to stay at Lyon|
|Ancelotti shrugging off Guardiola´s shadow|
|Uruguay international Lodeiro swaps Boca for Seattle|
|Ibrahimovic will bring United back to where they belong - Larsson|
|Transfer speculation frustrates Aubameyang|
|Willian ready for ´toughest Premier League season in history´|
|Astana 1 Celtic 1: Griffiths hits late equaliser|
|De Laurentiis feels betrayed by Higuain swapping Napoli for Juventus|
|Costa: Chelsea cannot be any worse than last season|
|Wilshere: Xhaka can hold Arsenal midfield together|
|Pato signs four-year deal with Villarreal|
|Higuain sets sights on Champions League after Juventus move|
|Lazio snap up Immobile from Sevilla|
|Batshuayi worth the money, insists Cahill|
|Arnautovic signs new Stoke deal|
|Smith leaves Liverpool for Bournemouth|
|Barcelona insist Arda Turan will stay|
|Andre Gomes: Barcelona suit my identity better than Real Madrid|
|Niersbach to appeal FIFA ban|
|Barcelona agree Mascherano renewal|
|Fernandinho can play in 10 positions - Guardiola|
|Reading´s kit launch is out of this world|
|Ben Arfa: I do not want to be PSG´s star player|
|FA Cup to trial fourth substitute|
|We want Balotelli and he wants us, says Besiktas chief|
|Crowd welcomes Higuain as he arrives for Juventus medical|
|Guardiola warns Man City stars: If you´re not fit, danger is coming|
|Mkhitaryan prepares to prove himself at United|
|Cavani: No pressure replacing Ibrahimovic|
|Wenger vows to keep transfer plans ´secret´ after Lacazette snub|
|Brannagan open to Championship loan move|
|Wenger wants to sign Mertesacker replacement|
|Ancelotti: Bayern´s transfer business done|
|Brisbane Roar sign former Danish international Kristensen|
|Verratti, Luiz missing for PSG|
|Sounders part ways with foundation coach Schmid|
|Mane turned down Manchester United for Liverpool|
|Zidane on Pogba: Until August 31, anything can happen|
|Mkhitaryan driven by father´s death|
|Inter rejected Napoli offer for Icardi, says president|
|Clichy: City fighting fit after Guardiola pizza ban|
|Everton and Burnley win as Hull are held|
|Ajax held by PAOK after Cillessen howler|
|Conte left frustrated by ´crazy´ money in transfer market|
|Neymar makes Barcelona case to Gabriel Jesus|
|Rostov comeback twice for Champions League draw with Anderlecht.|
|Arsenal defender Mertesacker set for lengthy lay-off|
|Conte not selling ´fantastic´ Matic|
|Ibrahimovic keen on MLS and Beckham´s Miami project|
|Neymar: I play for Messi, he´s the man|
|Barcelona reveal details of Andre Gomes deal|
|Suarez bullish over Barcelona prospects|
|Ajax claim Napoli keen on Milik to replace Higuain|
|Totti labels Higuain´s Juventus move ´a disaster´|
|Juventus confirm Higuain deal|
|Pato to Villarreal ´in the final stage´|
|PSG sign Lo Celso|
|Muller: Beating Dortmund will be more fun this season|
|Juventus sign Higuain from Napoli for €90m|
|Pastore: I´m like God in Paris|
|Injured Lanzini out of Olympics|
|Allegri unperturbed by Higuain fee|
|Menezes replaces Bento at Cruzeiro|
|Sporting rejected major bids from Inter and Liverpool for Joao Mario, claims father|
|Pochettino pleased by Tottenham despite Juventus defeat|
|Eriksson: Allardyce the right man for England|
|Mourinho makes United train after stepping off plane from China|
|Hazard can still match Messi, says Pedro|
|Pjanic shows there is life at Juve, with or without Pogba|
|Juventus 2 Tottenham 1: Benatia bags win for Serie A champions|
|Dembele: I am not the Bundesliga´s next superstar|
|Lyon claim €35m Arsenal offer for Lacazette rejected|
|Donnarumma dreaming of Milan captaincy as he eyes long-term stay|
|Robson: Ibrahimovic can match Van Persie´s first year at United|
|Rooney should remain England captain - Eriksson|
|Emery wants new striker at PSG|
|Santos accept Juventus bid for Gabriel|
|Eriksson expects Sweden to try and tempt Ibrahimovic out of retirement|
|Spurs signing Janssen almost quit|
|Leicester stay best for Mahrez - Ranieri|
|Allardyce to take Mourinho cue on Rooney|
|Ings ready to outdo big-money signings|
|Henderson optimistic over Liverpool campaign|
|Allardyce hardened to the challenge of England post|