Califf put Philadelphia (1-0-0) on the board after converting a rebound off a shot by Sebastien Le Toux shot and slamming it in. Le Toux's shot off the throw-in hit the right crossbar, but Califf was there to knock it in from inside the 6-yard box on the right side.
Houston (0-1-0) had several chances to tie the score, including a point-blank shot on a wide open net by Dominic Oduro in the 68th minute, but his shot from 8 yards out in the middle went over the net.
The Union had a chance to extend their lead in 56th minute, but Justin Mapp's shot from the right box was stopped by goalkeeper Tally Hall. Four minutes later, Danny Mwanga's shot from the right box went wide right.