The Vikings opened their season on the road against the St. Louis Rams and took the lead in the first half with a field goal in each quarter from 52 yards and 46 yards, respectively, from third-year kicker Blair Walsh and an eight-yard touchdown pass from Matt Cassel to Greg Jennings with 21 seconds left in the half, set up by an interception from Josh Robinson at the Rams' 35-yard line. The Rams struck back early in the third quarter with a field goal from Greg Zuerlein before Vikings wide receiver Cordarrelle Patterson made the play of the game with a 67-yard touchdown run. The Vikings secured the game late in the fourth quarter as TE Kyle Rudolph connected with Cassel on a seven-yard touchdown pass, while Rudolph's former Notre Dame teammate Harrison Smith took an interception 81 yards for the Vikings' fourth touchdown of the game. Zuerlein added another field goal late in the game to make the final score 34-6 to the Vikings, their first road victory since week 16 of the 2012 season against the Houston Texans.

Based on the above article, answer a question. Who caught the first touchdown of the game?
Greg Jennings