SAN FRANCISCO (AP) Rookie Daniel Mengden, with that quirky double-pump delivery and old-school handlebar mustache, thought his first major league win might come sooner than this as well as he had pitched so far.
He got promoted to the big leagues June 11, far sooner than expected - after just 43 outings in the minors. Even Mengden had figured he might reach Triple-A by midseason and perhaps earn a September call up from the Athletics.
Now, he's proving himself at the highest level. The 23-year-old pitched into the eighth inning for his first major league win Monday night, backed by Marcus Semien's three-run homer and four RBIs, and Oakland beat the San Francisco Giants 8-3 to open the Bay Bridge Series.
''My first win, it's a big one,'' he said. ''It took a little longer than I hoped. It's one of those, especially coming in the Bay Bridge Series, it feels really good to get the first win against them.''
Semien connected in the decisive second and Jed Lowrie and Khris Davis added RBI doubles against Jeff Samardzija (8-5) in that five-run inning, then Semien added a run-scoring double in the sixth. Davis hit an RBI single in the seventh.
Mengden (1-3) retired the first 13 batters in order before Angel Pagan's one-out single in the fifth. He called it a day after loading the bases in the eighth and losing his shutout bid.
The right-hander had pitched well enough to win during his initial three major league starts but Oakland scored only four runs total on those days. He had more than that when he took the ball to start the bottom of the second, leading 5-0.
''From the day he got here, he looked like he belonged,'' manager Bob Melvin said.
With his handlebar mustache resembling Hall of Famer Rollie Fingers' famous facial hair, Mengden allowed two runs and four hits in 7 2-3 innings, struck out five and walked three. He threw 10 of 14 first-pitch strikes to start the game. Traded by Houston to the A's last July, Mengden returned to his old wind-up delivery from his college days.
''It's my own, I guess, little flair,'' he said. ''It just helps my timing and gets everything going for me.''
Right fielder Billy Burns had a leaping catch on Denard Span's hard fly ball to start the fourth, while Mengden made a great play fielding Gregor Blanco's sharp comebacker for the final out of the second.
Oakland won for the fourth time in five games as Melvin called for his streaky club to keep some momentum and build some consistency. The A's earned just their third win in eight interleague games while handing the Giants just their third defeat in 16 games and fourth in 17 at AT&T Park.
Samardzija, who spent the second half of the 2014 season with Oakland after a trade from the Cubs, allowed six earned runs for the third time in his last five starts. He gave up eight hits in six innings, struck out two and walked two. The right-hander - signed to a $90 million, five-year deal during the offseason - is 1-3 over his last five starts after winning three consecutive outings.
''It's just about slowing the game down right now and making the pitch that needs to be made,'' he said.
In his previous start against Oakland last season with the White Sox, Samardzija surrendered a career-high 10 runs in three innings on Sept. 15.
The A's lead the all-time series against the Giants 55-52 since interleague began in 1997.
SWING AND A MISS
A's pitchers are 0 for 13 with eight strikeouts and two sacrifices in interleague play this season and 29 for 362 (.080) since the start of interleague play.
Athletics: RF Josh Reddick, out since May 20 with a fractured left thumb, had his day to be activated from the DL pushed from Monday to Tuesday as he didn't feel quite right and wanted one more rehab game with Triple-A Nashville. ... LHP Sean Manaea is set to come off the DL from a strained elbow in his start Wednesday against the Giants in Oakland.
Giants: SS Brandon Crawford got a day off to rest because of what manager Bruce Bochy called ''general soreness.'' ''We want to keep him fresh, stay away from injuries.'' ... RHP Sergio Romo (flexor strain in elbow) will have another rehab outing in the minors. ... Might Madison Bumgarner be allowed to hit during his Thursday start across the bay in the A's AL park? ''Too early to commit,'' Bochy said.
Athletics: RHP Kendall Graveman (3-6) lost in his only previous start against the Giants, a 4-3 defeat at AT&T Park on July 26, 2015.
Giants: Rookie RHP Albert Suarez (3-1) makes his fifth major league start and has allowed three or fewer earned runs in each of his 10 total outings.