Los Angeles FC midfielder Kellyn Acosta went from villain to hero in the final minutes as his team fought back for a 1-1 draw at the Philadelphia Union in their CONCACAF Champions League, semi-final, first leg on Wednesday.

Acosta had handled to give away a penalty which was converted in the 86th minute by Philadelphia's Daniel Gazdag but then popped up in the other area to level in the first minute of stoppage time.

Acosta's away goal gives LAFC the advantage heading into Tuesday's return leg in Los Angeles as the two American teams battle for the right to face Mexican opponents Tigres or Leon in the final.

The Union had the better of the chances throughout an often physical battle in what was a re-match of November's MLS Cup final which LAFC won on penalties after a thrilling 3-3 draw.

Argentine striker Julian Carranza hit the post from close range early in the contest after Gazdag had headed the ball across the box and it was Carranza who had the best opportunities for the home side.

The Union striker was unable to make the decisive contact when Jack McGlynn whipped in a dangerous, low cross in the 37th minute.

Then Carranza set Mikael Uhre free with a fine through ball but the Danish forward's low shot was well saved by LA's Philadelphia-born keeper John McCarthy.

The battle was in danger of spinning out of control when there was a mass scuffle after LA's Mexican forward Carlos Vela was hurt by a lunging challenge from Philadelphia defender Jakob Glesnes.

McCarthy than produced another save from a Carranza drive just before the interval.

Gazdag had the ball in the net in the 58th minute, tapping in after McCarthy had parried a Carranza drive but the effort was flagged offside.

LAFC struggled to create many openings but almost caught Philadelphia out when French-born striker Denis Bouanga found space and tested Union keeper Andre Blake.

Then came the late drama -- Mexican referee Cesar Ramos went to the pitchside monitor before ruling that Acosta had handled a fierce drive from McGlynn.

Hungarian midfielder Gazdag confidently converted what appeared to be the late winner for Philadelphia but Acosta had other ideas.

After a poor clearance from Philadelphia, Timothy Tillman crossed low from the right and Bouanga mis-kicked but central midfielder Acosta had burst into the box and drove his shot into the ground and up into the net.

LAFC are looking to reach the regional final for the second time where they could have a chance to avenge their 2-1 defeat in 2020 to Tigres.

"It wasn't the best performance, Philly did a great job of putting the game on their terms and being very direct," said LAFC head coach Steve Cherundolo.

"So we're ecstatic with the result ... one thing about this team, they find ways. I'm not concerned with the how as much as the results," he added.

Philly boss Jim Curtin said the late goal left his team with a tough task in the return.

"(It will be) hard, no question, but it's not impossible. My group right now is upset and angry, as they should be. Because we had a little lapse of judgment at the end of the game. But we'll regroup and go out to LA and make the city proud," he said.

Tigres lead Leon 2-1 after their first-leg on Tuesday and will meet again in the return on Wednesday.