Giants: Belt came out of the game after just three innings with a stiff neck, a precautionary measure, according to Giants manager Bruce Bochy.
Left-handed setup man Jeremy Affeldt is due to pitch one inning in a B game against the Chicago Cubs in Mesa on Monday.
Diamondbacks right fielder Gerardo Parra didn't wait long to show off his NL Gold Glove defensive ability.
When the Giants' Angel Pagan led off the bottom of the first with a single to shallow right and strayed a bit too far off first base while making the turn, Parra made him pay by throwing him out.
Right-hander Brad Ziegler, who was 8-1 and saved 13 games for Arizona when he assumed the closer's role in the second half of 2013, had a rough outing against the Giants. He took the loss after giving up four earned runs on four hits in two-thirds of an inning.
Meanwhile, right-hander Addison Reed, expected to be the closer this year after being acquired in a trade after saving 40 games for the Chicago White Sox, pitched the sixth inning and gave up a double to Gregor Blanco before getting a strikeout to end the inning.