The finale of the two-leg, total-goal series is scheduled for February 27 in Chester, Pa. The sides are vying for the right to oppose Mexico's Pachuca in the round of 16.
The Union trailed 1-0 at half-time following a 28th-minute own goal from Jakob Glesnes. Carranza pulled Philadelphia level with a header in the 55th minute, then put the Union on top by completing an impressive team passing sequence with a tap-in goal in the 75th minute.
Four minutes later, Philadelphia's Quinn Sullivan raced down the right flank, then cut back a pass to Daniel Gazdag, who laid the ball off for Carranza to finish with a goal from 12 yards.
Gerald Taylor halved Saprissa's deficit entering the second leg by scoring in the 90th minute.
St. Louis City 2, Dynamo 1
Hosei Kijima scored the match-winning goal in the 90th minute as host St. Louis City topped Houston in the first leg of a CONCACAF Champions Cup first-round series.
Earlier in the second half, St. Louis' Tim Parker scored the opening goal before Houston's Sebastian Kowalczyk equalized.
The teams will conclude the two-leg, total-goal set on February 27 in Houston. The victor will advance to meet the reigning MLS Cup champion Columbus Crew in the round of 16.
On the decisive play, a St. Louis City cross wasn't dealt with properly in the six-yard box by a Dynamo defender. Kijima pounced on the loose ball and rolled a 12-foot shot inside the far-goal post.
In the 61st minute, St. Louis City's Indiana Vassilev whipped a left-footed free kick from 30 yards out on the left side into the middle of the penalty area. Parker outran his defender to the ball and powered his header just past Dynamo goalkeeper Steve Clark to the bottom right corner.
Eleven minutes later, Houston's Ibrahim Aliyu broke down the right flank and rolled a cross to the top of the six-yard box. Kowalczyk ran forward and knocked in a right-footed shot to level the match.
