PHOENIX -- Manager Gabe Kapler wore a big grin across his face during postgame interviews on Sunday night. The fact that his San Francisco Giants had won their third straight game was just a small part of the reason.

Anthony DeSclafani threw 8⅔ effective innings, Austin Slater and Darin Ruf both homered and the Giants beat the Arizona Diamondbacks 5-2. But the most important moment of the night might have been back in the medical room, where X-rays on All-Star Buster Posey's left thumb were negative.

"You see me smiling," Kapler said. "That's my level of relief."

The Giants said that Posey has a left thumb contusion after leaving the game in the sixth inning. The 34-year-old catcher took an awkward shot to his glove hand on a foul tip by Daulton Varsho.

Posey immediately jumped up and walked to the mound, shaking his hand. He caught a couple practice pitches from DeSclafani and then tried to remain in the game. The next pitch was a full-count strikeout of Varsho, but TV replays caught the normally stoic Posey grimacing after he caught the ball.

After that, he took himself out of the game, walking off the field and into the dugout. He was replaced by Curt Casali.

Kapler said Posey won't start Monday's game against the St. Louis Cardinals, but said it's possible Posey could be available off the bench.

Posey, who was recently named to his seventh All-Star team, had two runs, one hit, one RBI and a walk before exiting. He came into Sunday's game batting .327 with 12 homers.

The Associated Press contributed to this report.