SEATTLE -- Left-hander Jason Vargas was supposed to have an extra day between starts to rest an arm that seemed to be getting a little weary.

His next start originally was scheduled for Sunday.

But when Erik Bedard had to be placed on the 15-day disabled list, Vargas returned to his normal routine, started on schedule Saturday night and pitched lights-out in the Mariners' 7-3 Interleague victory over the D-backs before 29,525 at Safeco Field.

Wladimir Balentien, who will get a good look as a potential mainstay in left field following the loss of Endy Chavez to a season-ending knee injury, responded well in his first crack, launching a solo home run in the fourth inning to give Seattle a one-run lead, and ended the game with a nice catch, lunging into the stands to snare a foul ball.

"It was nice to see him step up, on offense and defense," manager Don Wakamatsu said.

Vargas did some big-time stepping up himself.

It didn't look promising when two of the first three batters Vargas faced reached on base hits and one of them scored. But the next 17 batters were retired in order and the only other hit the lefty allowed through seven innings was a game-tying solo home run in the seventh to Justin Upton.

Vargas departed at the end of the inning, and in a repeat performance of Friday night's series-opening win, the Mariners' offense came to life, scoring two runs in the seventh inning and three more in the eighth to secure the win and climb back to .500 at 34-34.

"I thought Vargas threw a great game, as good, or close to, the game he threw in Anaheim," Wakamatsu said. "He looked sharp, he looked fresh."

Indeed, Vargas looked like the same guy who held the Angels to four hits and two earned runs in his May 29 start, and not anything like the pitcher who was rocked for 12 hits and seven runs in his previous outing.

This performance might have been his best overall outing of the season as Vargas struck out four and had his second walk-free outing since joining the starting rotation in mid-May.

"He got a lot of first-pitch outs," catcher Rob Johnson said. "This team likes to swing. They were putting the bat on the ball, but were hitting 'em right at our guys."

Johnson gave high marks to Vargas' sinker and changeup.

"He made his changeup work and when you can do that," Johnson said, "your fastball is going to be more effective."

The battery had praise for each other.

"It's nice having Rob back there tonight," Vargas said. "He's caught the majority of my starts and we just really went over the game plan before and got a pretty good idea of what I could do."

The key was changing speeds and keeping the free-swinging D-backs off balance.

Vargas retired the last two batters he faced in the first inning and didn't allow another runner until the seventh, when Upton drilled a first-pitch fastball over the left-field fence.

"He had swung at the first pitch in his first two at-bats and we thought he might take the first one this time," Johnson said. "It's not like [Vargas] was trying to throw it down the middle, but he pulled the pitch a little and it went right down the middle."

Upton was waiting and pounded the pitch for his 13th home run.

The Mariners, who scored four runs in the eighth inning to win Friday night's game, went on the offensive an inning earlier, loading the bases with none out in the seventh inning and settling for two runs.

Designated hitter Mike Sweeney hit a sacrifice fly to score the go-ahead run and Franklin Gutierrez hit a run-scoring single up the middle.

Balentien's second home run of the season -- his first since April 25 -- gave the Mariners a 2-1 lead in the fourth inning, but Upton hit a first-pitch home run to left field leading off the seventh inning to tie the game.

The no-doubt-about-it blast ended Vargas' streak of 17 consecutive batters retired.

The only two hits Vargas surrendered in the first six innings set up the first run of the game.

The D-backs had runners on first and third bases via singles with one out in the first inning when Mark Reynolds fouled a 3-and-0 pitch behind the plate.

Johnson made the catch about halfway between the plate and the screen. Upton tagged up at first and high-tailed it to second. Johnson peeked at third base, where Felipe Lopez was stationed, and threw the ball to second.

The throw was low and skipped past shortstop Yuniesky Betancourt and into center field, allowing Lopez to score.

The Mariners pulled even in the third inning when, after a rare four-pitch walk to Betancourt, Ichiro Suzuki singled into center field. Upton bobbled the ball, enabling Betancourt to score.

Mariners third baseman Adrian Beltre, who jammed his shoulder diving into second base in Friday night's game, was lifted for a pinch-hitter in the seventh inning when the shoulder stiffened. He might be able to play in Sunday's series finale which features ace right-hander Felix Hernandez gunning for his eighth victory.