The win clinched FC Dallas (8-5-7, 31 points) a spot in the MLS Cup playoffs for the third consecutive year. Dallas is 3-1-1 over its last five games, a late-season surge that has the club contending for a top-four finish in the Western Conference and a potential home playoff date.
The defeat officially eliminates Houston (4-9-9, 21 points) from playoff contention. The Dynamo have now missed the postseason six times in the last seven seasons.
After scoring just once in his first 16 games with FC Dallas, Picault delivered a breakout game. Picault converted an Andres Ricaurte cross in the 27th minute, then scored on a breakaway three minutes into stoppage time.
Franco Jara opened the scoring for FC Dallas, putting the final touch on a Michael Barrios header in the 19th minute. It was Jara's seventh goal of the season, and the forward's second in as many games.
Houston is winless (0-2-4) in its last six games and 1-7-5 in its last 13 games. The Dynamo's struggles were apparent on Saturday as they managed only two shots on goal and didn't do much with their chances.
The Dynamo's best opportunity came on a Memo Rodriguez cross into the box in the 87th minute that went untouched by a Houston player.
Jimmy Maurer made two saves for the Dallas goalkeeper's sixth shutout of the season.
FC Dallas defender Bryan Reynolds had to leave the game in the 44th minute due to a possible concussion. Reynolds has established himself as a key member of the Dallas back line since becoming a starting fullback last month.
FC Dallas claimed the Texas Derby for the eighth time in club history against their local rivals. Dallas went 2-1-1 in four games against Houston this season.