SAN FRANCISCO -- On his 26th birthday, Landen Roupp got to celebrate another big milestone: his first big league start.

Another Giants rookie -- Hayden Birdsong -- was originally supposed to pitch on Tuesday night, but the Giants decided to push him back two days to give him a bit of extra rest. That created an opportunity for Roupp, who overcame a shaky first inning to deliver five solid frames in a series-opening 3-2 loss to the Brewers at Oracle Park.

Jackson Chourio sent Roupp’s first pitch of the game to right field for a leadoff double, and the Brewers quickly built a 2-0 lead behind RBI singles from William Contreras and Willy Adames. But Roupp managed to settle in after that, retiring 13 of the final 14 batters he faced to hold Milwaukee to two runs on five hits over a career-high five innings.

“I couldn’t have a better birthday present,” Roupp said. “I felt really good. I felt like I pounded the strike zone. The first inning, I let a couple of pitches leak over the zone, and they got some early hits. But after that, I felt like I locked in and settled in and got to it.”

Roupp struck out three and walked none in the 68-pitch effort, leaving his ERA at 3.44 over 20 Major League appearances this year. A little over half of Roupp’s offerings (51%) were curveballs, which generated each of his seven whiffs against the Brewers.

Roupp’s electric breaking ball was one of the reasons the Giants decided to carry him in their Opening Day bullpen even though the young right-hander had never pitched above Double-A Richmond prior to this season. Still, his struggles to consistently locate his sinker ultimately prevented him from staying in the Majors for the entire year, as he was sent down to Triple-A Sacramento after recording a 6.06 ERA with 10 walks and 15 strikeouts over 16 1/3 innings in his first 11 outings.

The results have been far more encouraging since Roupp was recalled last month, as he’s allowed only three earned runs over 20 1/3 innings (1.33 ERA) over his last nine appearances.

Opposing hitters entered Tuesday batting only .190 (4-for-21) against his curveball and .095 (2-for-21) against his sinker since Aug. 9, which compelled the Giants to finally give him a look in their rotation.

“Much better here recently,” manager Bob Melvin said. “It was walks early on and getting behind in counts and not really throwing his fastballs for strikes. Here recently, he’s been doing that, which keeps everybody off his offspeed stuff. Throwing some changeups, some harder breaking balls, too. But early on, it was mostly curveballs, which was his pitch, whether for strikes or chase. He had trouble throwing fastballs for strikes. Now he’s doing both. He has the repertoire. He’s been a starter before. We like him both ways, but it was good to see him stretched out some and give us five innings and certainly keep us in a game.”

Roupp said he’s still working on developing his other pitches to round out his arsenal and show that he’s capable of sticking as a starter over the long run. He found a new grip for his changeup this year -- it’s similar to the one employed by Logan Webb -- and also plans to mix in more of his slider and four-seamer moving forward.

“I think it’s just showing other pitches,” Roupp said. “The changeup has come a long way. But really, if I have my two-seam going, the curveball plays really good off that. Just spotting both of those pitches and adding the slider and the four-seam next year and stuff like that, I think it will be a real good help.”

Tristan Beck replaced Roupp in the top of the sixth, but he surrendered a leadoff homer to Garrett Mitchell that stretched the Brewers’ lead to 3-1. Mike Yastrzemski homered in the bottom half of the inning to pull the Giants within one, but they came up short after Brewers closer Devin Williams struck out Tyler Fitzgerald to leave a pair of runners stranded in the bottom of the ninth.

“Offensively, we didn’t do enough,” Melvin said. “Four hits isn’t going to win you too many games, even though we scratched a couple of runs out of it.”