Sandoval inadvertently kicked Velasquez in the neck. It was that kind of day for the Astros.
"He pounded the strike zone with a couple different pitches," Astros manager A.J. Hinch said. "He had a really good changeup, a really good cutter. This game was almost entirely about him."
It was a rare day of frustration for Houston, which entered on a five-game winning streak and only 14 hours after a 12-8 comeback victory Friday night in 10 innings.
Collin McHugh (9-4) was denied a fourth straight win, giving up four runs — three earned — and seven hits in 5 1-3 innings. Xander Bogaerts delivered an RBI single in the first and a run-scoring double in the fifth off the right-hander after catcher Hank Conger's throwing error.
Mookie Betts' RBI double came on the final pitch for McHugh, who walked three and struck out one.
"Fastball was sporadic, especially early on," McHugh said. "I threw more off speed today, cutter, curveball. Especially at the top of the lineup, they put together some good at-bats against me."
Houston's offense, which a night earlier had 10 players score, was quieted by Buchholz (7-6). The right-hander struck out five through three innings, set down 12 straight and won his fifth straight decision.
Three of Buchholz's eight strikeouts came against Colby Rasmus in his return from injury.
"He looks fine and he was moving around fine," Hinch said. "It was more about Buchholz and less about Colby. I think he was a tough matchup for all our guys."
Velasquez was sporting two large scratches on the left side of his neck in the clubhouse after taking Sandoval's right cleat in the head on Preston Tucker's foul pop in the fourth.
Three innings later, Sandoval started a nifty double play while playing on the right side in a shift against Valbuena.
"We've been playing good baseball," Conger said. "So for (Buchholz) to go out there and play the way he did right there, hats off. Just move on to Sunday."
Astros: Rasmus started in center field in his first game since June 26 due to a skin infection. ... OF Jake Marisnick (hamstring) arrived in Boston following a minor league rehab stint and was activated from the disabled list after the game. OF Domingo Santana was sent to Triple-A Fresno.
Red Sox: 2B Dustin Pedroia, on the 15-day DL with a strained right hamstring, hit in the cage after increasing his running a day earlier. Manager John Farrell said the club is still trying to decide if Pedroia will be activated for a series against the New York Yankees next weekend.
Hinch said RHP Dan Straily, who started Friday, will get a second start Wednesday in Cleveland. But the Astros will soon have to make a number of roster moves as they get healthier.
"We're going to start sending down guys who are producing," Hinch said.
Astros: RHP Lance McCullers (4-2) is slated to start the series finale Sunday. He threw seven innings of one-run ball in a win over Kansas City on Wednesday.
Red Sox: Rookie LHP Eduardo Rodriguez (4-2) is scheduled to start. He's allowed one run or none in four of his six starts.