Madison Bumgarner’s mere presence back on the mound and healthy after all these months meant so much to the San Francisco Giants, even in defeat.But the big lefty is a perfectionist, and he expected more of himself in his long-awaited season debut. Bumgarner pitched six strong innings yet the Giants missed key scoring opportunities in losing 3-2 to Patrick Corbin and the Arizona Diamondbacks on Tuesday night as San Francisco’s five-game winning streak was snapped. “That’s what I get paid to do,” Bumgarner said. “It’s nice to earn your paycheck instead of stealing it.” Bumgarner (0-1) broke the pinkie on his pitching hand during his final start of spring training, then finally got his turn in early June for an adoring home crowd. He allowed two runs and eight hits in his first regular-season outing. San Francisco’s ace left-hander struck out three and didn’t walk a batter. Corbin (6-2) outdid MadBum, striking out seven over 6 1/3 innings and allowing one run on four hits with two walks. The left-hander was staked to an early lead and the first-place Diamondbacks held on late.Buster Posey hit an RBI single with two outs in the ninth and Andrew McCutchen followed with a single before Brad Boxberger retired Evan Longoria on a groundout to earn his 14th save. Bumgarner had so hoped to start this season on a positive note after he missed nearly three months in 2017 following an April 20 dirt bike accident sustained during an off day in Colorado. But after breaking his left pinkie in March when it was hit by a line drive, he underwent surgery to have three pins inserted and then later had them removed.