LAFC ended up beating the Philadelphia Union in penalty kicks to secure the title ... and JB was clearly on pins and needles as the drama unfolded.

Bieber and his wife, Hailey, sat among the normies throughout the game ... and after the home team came away with the 'ship, Justin lifted her up in celebration.

Biebs even had his own custom LAFC jersey for the game ... draping it over his head as he cheered on his squad.

Justin and Hailey weren't the only A-listers in attendance -- Magic Johnson and Will Ferrell, who are co-owners of the team -- were also at Banc of California Stadium for the matchup.

It was a busy weekend for the duo -- as we previously reported, they were living it up at Odell Beckham Jr.'s birthday bash later that night.