PHILADELPHIA -- It was looking like a potentially lost season for Daniel Mengden.

The Oakland prospect, who was the winning pitcher in the A's 4-0 victory over the Philadelphia Phillies on Friday night, suffered a foot injury in February that cost him most of spring training. Then after working his way to the majors in May, a June rib injury set him back.

When he got back to the minors in August, he was unable to go any more than five innings and couldn't keep his pitch count down.

"First couple (starts) weren't very good," he said. "Just getting back in the swing of things, jitters, a little bit, I was kind of wild and kind of sporadic."

But given another chance to show what he can do at the highest level, Mengden isn't letting the last few weeks of the 2017 MLB season go to waste.

Backed by two early home runs in his latest outing, Mengden turned in the most dominant outing of his young career, going the distance as the A's blanked the Phillies at Citizens Bank Park.

Though Mengden (1-1) entered with a 7.07 ERA in three big-league starts scattered over the course of the season, the 24-year-old right-hander absolutely shut down a Phillies offense that had put up 27 runs in its previous three games.

Mengden needed 118 pitches to throw his first career complete-game shutout, striking out seven -- including the last two batters he faced -- while giving up just two hits without issuing a walk.

"It felt great," he said of going the distance. "We dream about doing it since we're little and coming all the way up and doing it is a great feeling."

The Phillies (57-90) only had one runner get past first base all night, and only left one man on base. Rookie shortstop J.P. Crawford had the team's only two hits, going 2-for-3.

"Mengden really stymied us," Phillies manager Pete Mackanin said. "He pitched backwards, threw as many offspeed pitches as fastballs. Give him credit.

"Glad I didn't give Crawford the night off."

It was a statement outing from Mengden, the former fourth-round draft pick of the Houston Astros in 2014.

After failing to go more than five innings in any of seven minor league starts in August and early September, Mengden has now thrown 14 innings while giving up just two earned runs in two starts with the A's (65-82) in the past week.

"He had some injuries and couldn't sustain anything for any length of time, and was giving us five, maybe six innings," A's manager Bob Melvin said. "To go nine innings like that should do the world for his confidence."

Mengden also picked up his first career hit, a hard-hit ground-ball single into left field that just barely got past Phillies shortstop J.P. Crawford in the second inning. He then scored his first run, coming around to touch home on Matt Joyce's second-inning home run.

"You don't get to hit in the AL ... but I love hitting," Mengden said. "Just tried to get a good pitch to hit, close my eyes and swing and see what happens."

A's first baseman Matt Olson put his team on the board in the first inning with a two-run shot to right, his 19th home run of the season. It's the eighth homer of the month for the rookie, one of four players in the Oakland lineup in either his first or second year in the majors.

Joyce's 24th homer of the year came on a first-pitch fastball and found the second deck in right field at Citizens Bank Park.

That was all the offense the Athletics needed to pick up their seventh win in their last 10 games.

Phillies starter Mark Leiter Jr. (3-6) took the loss, though he settled in nicely after the two home runs.

Leiter Jr. tied his career high with nine strikeouts, giving up seven hits and four earned runs plus one walk as his ERA climbed slightly to 4.93.

"I thought the two homers put us in a tough hole early on," he said. "That was disappointing. After that, I tried to keep us in it."

NOTES: The series continues Saturday as Phillies RHP Ben Lively (3-6, 3.86 ERA) takes on A's RHP Kendall Graveman (5-4, 4.48). First pitch is scheduled for 7:05 p.m. ET. ... This is only the sixth-ever series between the A's and Phillies. They shared the city of Philadelphia from 1901 to 1954 before the A's left for Kansas City and then Oakland in 1968. ... The A's moved to 2-2 on their nine-game road trip, which began in Boston (1-2) and concludes in Detroit next week. ... The Phillies have the worst interleague record in the majors this season (4-14). Oakland (6-12) had been tied for second worst entering the evening.