PHOENIX — Despite all the throaty pleas to promote Buster Posey, perhaps there is another hyped prospect on the farm that could make an immediate improvement for the Giants.

Or has everyone forgotten about Madison Bumgarner?

It isn't a stretch to think Bumgarner might be close to reclaiming the rotation spot he lost this spring, especially after Todd Wellemeyer gave up the launch codes in a 13-1 loss to the Arizona Diamondbacks on Wednesday night.

Wellemeyer (2-4) gave up three home runs in his five innings, and the Diamondbacks hit three more crackling shots off the Giants bullpen. And the cruelest part for Giants fans: Adam LaRoche was the man who opened and closed the power parade.

In case your hot stove is no longer piping, recall that LaRoche is the slugger who turned down a two-year, $17 million offer from the Giants to sign a one-year, $6 million deal to play in Arizona's more hitter-friendly climes.

You could say it has been a while since the Giants gave up six homers in a game. The last time it happened, there was an intern at the White House named Monica Lewinsky.

It was April 19, 1996, when left-hander Allen Watson gave up five long balls to the Cubs at Wrigley Field, then didn't endear himself to the locals when he called for a public torching of the Friendly Confines.

There was nothing friendly about Chase Field when the Giants arrived. LaRoche's solo shot tied it in the second inning, Justin Upton connected to lead off the fourth, and Stephen Drew hit a three-run shot in the fifth.

Chris Snyder added a two-run shot off right-hander Denny Bautista, and Brandon Medders allowed two more homers in a six-run eighth inning. Kelly Johnson crushed a hanging breaking ball, and LaRoche drove one above the yellow line as the last-place Diamondbacks showed plenty of muscle in the first meeting of 2010 between the two NL West clubs.

Entering the game, the Giants' staff had allowed the fewest home runs in the major leagues. That's not a distinction it held at the end of the evening.

Wellemeyer has allowed nine home runs; the Giants' other four starters have combined for 10.

Wellemeyer was coming off an effective outing against the weak-hitting Houston Astros, but he has a 5.70 ERA and the Giants are 2-6 in his starts. He also has been woeful in his four road starts, posting a 9.34 ERA while walking nearly one per inning.

The Giants are off Monday, when it would be Wellemeyer's turn to pitch again. They could decide to skip him and use him in the bullpen, but they would need a fifth starter again May 29 against the Diamondbacks.

Freddy Sanchez didn't make an impact in his season debut, going 0 for 4 while making two outs in the air, one on the ground and striking out in his first at-bat.

But there might have been one hopeful sign for the Giants' tweaked lineup, as new cleanup man Pablo Sandoval made much better contact.

Sandoval had been 0 for 15 with two out and runners in scoring position before he whistled a line single past Kennedy's ear to score Aaron Rowand, who had doubled to lead off the game.

Sandoval also hit a ground-rule double in the seventh inning.