Philadelphia Union will have to overturn a first-leg deficit to progress past the Champions Cup last 16 after a 1-0 loss to Club America at Subaru Park.

Raphael Veiga's 20th-minute strike was enough to separate the two sides on Tuesday, though the Union squandered multiple chances to level the tie in front of their home fans.

After a quiet start from both teams, Veiga scored with the first shot of the match. He flicked up a pass from Brian Rodriguez before lashing his powerful attempt in off the crossbar, leaving Andrew Rick with no chance of making a save.

The visitors went close to making it 2-0 just after the hour mark when Rick almost spilled an attempted catch from Alex Zendejas' shot into his own goal, while Ezekiel Alladoh shot just over the bar at the other end on the stroke of half-time.

Bruno Damiani failed to hit the target after being picked out by Frankie Westfield's cross before Indiana Vassilev fired just wide of the left post from the edge of the box as Philadelphia upped the pressure.

Vassilev then perhaps missed the Union's best opportunity to equalise in the 86th minute, shooting well wide of the target despite the goal being at his mercy following a good tackle by Milan Iloski.

Reigning champions Cruz Azul managed to complete a late 3-2 victory over 10-man Monterrey in their last 16 first leg.

After Roberto de la Rosa's brace gave Monterrey a 2-1 lead at the break, Santiago Mele's red card turned the game on its head, with Gonzalo Piovi and Nicolas Ibanez securing the turnaround win.

Data Debrief: Vassilev does the hard work but fails the easy part

Bradley Carnell will be left wondering how his side did not score in this first leg, with the Union producing 1.73 expected goals (xG) from 12 shots to Club America's 0.59 from seven attempts.

Vassilev may go on to be haunted by his late miss, but he made a positive impact off the bench nonetheless. He registered the joint-most shots in the match (three), which amounted to 0.51 xG, while he also created a match-high four chances from just six completed passes.

Philadelphia have now lost three consecutive matches in all competitions, and have scored just once across those defeats.