Gregg Popovich has been coaching the Spurs for 23 years. He's never had a season this bad. San Antonio is 10-15. The Spurs are even worse against the spread at 6-18-1 (25 percent), which is the worst ATS mark in the NBA. 
Houston is one of the best teams in the NBA. Yet when these teams last met two weeks ago in San Antonio, the Spurs won in double overtime, 135-133. The Rockets blew a 22-point lead in that game. That was also the game where the officials' mistakenly waved off James Harden's slam dunk basket. It was the most frustrating and controversial game of the season for the Rockets. 
Now Houston gets its chance for revenge. 
The Rockets not only are thirsty for payback, but they are off a surprising home loss to the Pistons this past Saturday. San Antonio is off an overtime victory against Phoenix also on Saturday. That game, though, was played in the high elevation of Mexico City. It was the fourth straight overtime game for the Spurs. 
So San Antonio could have a fatigue issue especially after playing Mexico City. The Spurs have failed to cover 17 of the last 21 times after a victory. 
The Rockets have a monster edge in the backcourt with James Harden and Russell Westbrook, while Clint Capela can hold his own in the frontcourt against the Spurs' big people.