"To get some run support and know the team has got your back, especially going down 2-0, it's a big deal," Milone said. "It kind of lit a fire under my butt and told me that I needed to keep this game close."
"If there's anybody that can recover from a little bit of a difficult start, it's Tommy," A's manager Bob Melvin said. "He doesn't let too much get to him. He just concentrates on where he's throwing that particular pitch and doesn't get too far ahead of himself."
The A's had seven extra-base hits overall: five doubles and two home runs. Eight A's had at least one hit while four drove in at least one run.
Milone (1-0) allowed only one baserunner after the second inning, finishing with a walk and four strikeouts. Sean Doolittle pitched the eighth, and Chris Resop worked the ninth to complete the five-hitter.
Lowrie, acquired in a trade from Houston just before the start of spring training, went 3-for-3 with a walk and three RBIs. His tiebreaking two-run double off Saunders in the fourth put the A's ahead for good.
Gutierrez got the Mariners off to a nice start when he hit the fourth pitch from Milone over the wall in left for his second career leadoff homer. Morse, a key offseason acquisition for Seattle, tacked on a two-out drive to center for his third homer in two games.
Freiman's first career hit got Oakland on the board in the second. But the rookie first baseman was thrown out at the plate trying to score on Scott Sizemore's double to left.
Freiman later singled in the fourth, then made a sliding catch in front of the photographer's well near Seattle's dugout in the fifth.
Saunders (0-1) ran his pitch count up in the third when he yielded a leadoff double to Coco Crisp, then walked Lowrie and Young. Yoenis Cespedes drove in Crisp with a sacrifice fly to center, but Saunders retired the next two batters to end the threat.
"(Saunders) just didn't have the command of the secondary stuff he typically has," Seattle manager Eric Wedge said. "He controlled damage about as well as he can, considering everything. He was just never able to lock it in."
The A's went up 4-2 in the fourth on Lowrie's double to left-center after Josh Reddick doubled and Crisp reached on a fielder's choice.
Lowrie and Young added consecutive home runs off Kameron Loe in the seventh.
Milone, tied for the team lead in wins as a rookie last season, and two relievers did the rest.
Milone gave up a leadoff single to Jesus Montero in the second, then walked Jason Bay before getting Robert Andino to hit into a double play. Seattle didn't get a runner past first base the rest of the game.
Sizemore went 1-for-4 in his first game since he injured a knee on the first day of spring training in 2012. ... Saunders lasted four innings and allowed seven hits with four walks. ... Seattle has not started a season 3-0 since 1995. ... The A's claimed RHP Will Harris off waivers from Colorado and optioned him to Triple-A Sacramento. To make room on the 40-man roster, RHP Josh Stinson was designated for assignment. ... RHP Brendan Maurer will make his major league debut for Seattle on Thursday. He'll oppose Oakland RHP A.J. Griffin, who went 2-0 with a 1.64 ERA in two starts against Seattle in 2012.