OAKLAND, Calif. -- At this rate, Athletics manager Bob Melvin is going to have a hard time leaving Mark Canha's name out of the lineup, no matter the matchup.

The Oakland rookie is off to a fast start this season and Melvin wants Canha to soak it all in.

Canha hit his first major league home run to back a three-hit shutout by Drew Pomeranz and two relievers, and the A's beat the Seattle Mariners 12-0 on Friday night.

Overall, Canha is hitting .500 (7 for 14) with six RBIs.

"It's pretty unbelievable for a number of reasons," Melvin said. "He's earned his time, no doubt. He's swinging the bat great for us."

Canha, who came within inches of hitting a grand slam on Wednesday, went 3 for 5. He reached on an infield single and scored on Ben Zobrist's double in the first. His homer off Walker in the second came on a 2-0 pitch and landed halfway up the bleacher seats in left.

"It's three games," Canha said of his start. "I'm just trying to take it one day at a time. When you're locked in, it doesn't matter who you face sometimes."

Ike Davis drove in four runs and Sam Fuld added three hits for Oakland.

The A's continued their pattern of an on-again, off-again offense by knocking around Mariners starter Taijuan Walker and three relievers. In its three wins this season, Oakland has outscored its opponents 30-0.

Zobrist doubled twice while Marcus Semien added two hits, both coming in the fourth when Oakland scored six times to break the game open.

Pomeranz (1-0) beat out Jesse Chavez for the fifth spot in the A's rotation and showed why in his first start of the season. He gave up just two hits and faced only one batter over the minimum through seven innings.

The Oakland left-hander struck out six and didn't allow a baserunner until Austin Jackson's single to left with one out in the fourth. He promptly got Robinson Cano to hit into a double play on the next pitch, then set down the next seven Mariners.

Fernando Abad pitched the eighth while R.J. Alvarez worked the ninth to complete the shutout.

The A's early offensive outburst helped.

Walker (0-1), who went 4-0 with a 0.67 ERA in the spring, was roughed up. He gave up nine runs and nine hits in 3 1/3 innings with three strikeouts and two walks.

"We were on the receiving end tonight," Seattle manager Lloyd McClendon said. "We'll hand out a few. It was just their night."

HELMET PRIDE

A football helmet from Michigan hung in Pomeranz's locker after the game. It was a gift to the team from Wolverines coach Jim Harbaugh, who visited the A's during spring training. Melvin has decided to occasionally award the helmet to players for their performances. "I'm the first recipient," Pomeranz said, grinning.

TRAINER'S ROOM

Mariners: OF Seth Smith sat out his third straight game with a groin strain but McClendon is hopeful of getting Smith back in the lineup Saturday.

Athletics: The team has pushed back plans to activate OF Josh Reddick from the disabled list. Reddick will play at least one more game in the minors before rejoining the big league club. ... Closer Sean Doolittle has extended his long toss workouts to 90 feet. ... LHP Barry Zito gave up five runs and 10 hits in his first minor league start for Triple-A Nashville.

UP NEXT

Mariners: RHP J.A. Happ makes his Seattle debut on Saturday against Oakland. The former Toronto Blue Jays pitcher won his only start against the A's in 2014.

Athletics: RHP Sonny Gray (1-0) makes his second start of the season and eighth of his career against Seattle. Gray carried a no-hitter into the eighth inning against Texas on opening day and has an 18-inning scoreless streak going.