Kaan Ayhan scored with the final kick of the match as Turkey posted their only win of the World Cup.
Auston Trusty scored in the third minute and Sebastian Berhalter levelled early in the second half on Thursday (Friday AEST) for the Americans, who had already won Group D with victories over Paraguay and Australia.
Coach Mauricio Pochettino's team will meet Bosnia-Herzegovina in the round of 32.
Pochettino fielded nine new starters in Inglewood and Christian Pulisic entered in the 58th minute. He hadn't played since the first half of the Americans' opener due to a calf injury.
Arda Guler and Orkun Kokcu scored in the first half for Turkey, who had already been eliminated after losing their first two matches despite largely dominating both statistically.
The Europeans won in the eighth minute of added time when Can Uzun got the ball in space on the back post and pushed it past sprawling goalkeeper Matt Turner to Ayhan, who slid to knock it home.
The Los Angeles crowd was still chanting and standing when Berhalter airmailed a long corner to Trusty, who made the stadium shake when he banged it home inside the back post.
Trusty's goal was the Americans' seventh of the tournament, tying their scoring record for any World Cup before knockout play can even begin.
It was the 173rd goal of this tournament, breaking the record for the most combined goals scored in a World Cup set in Qatar four years ago - and doing it in four fewer matches.
Turkey levelled in the 10th minute when Baris Alper Yilmaz teamed up with Guler, the 21-year-old Real Madrid star.
Güler then set up another goal in the 31st minute with a pass that eventually led to Kökçü's close-range shot.
Berhalter equalised in the 49th minute by running onto a loose ball about 20 yards from the net for a vicious strike.
Pulisic replaced Tim Weah in the 58th minute for his first action since the first half of their 4-1 victory over Paraguay nearly two weeks ago.
The AC Milan midfielder came on to an enormous roar and created a scoring opportunity just a couple of minutes later with a dynamic run down the left side.
Pulisic nearly scored again in the 63rd minute, but his quick shot off a nice pass from Berhalter was knocked off the goalpost by Turkey goalkeeper Ugurcan Cakir, with Brenden Aaronson botching the resultant sitter.
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