MINNEAPOLIS(AP) With each Oakland drive that soared over the outfield wall at the Metrodome on Friday, Clayton Mortensen felt a little more comfortable.

That comfort translated into the first major league victory for one of the Athletics' top pitching prospects.

Mortensen, acquired in the trade that sent Matt Holliday to St. Louis, limited the Minnesota Twins to one run on five hits over six innings as the Athletics rolled to a 12-5 victory.

Jack Cust , Mark Ellis , Cliff Pennington , Daric Barton and Kurt Suzuki all homered for an Oakland team that entered the game last in the American League in home runs.

When the game was over, however, no Oakland player had a bigger smile on his face than Mortensen. The 24-year-old, who saved the official lineup card and the red cap that teams wore in honor of the anniversary of the September 11, 2001, terror attacks, finally felt like he was able to throw his fastball, curveball and changeup well in the same game.

''Once I can get that perfected, the confidence just goes up,'' said Mortensen, who was making only his third start and fourth major league appearance. ''Being able to see that I can get a win against a team like this, a really potent hitting team, definitely helps out.''

And unlike in his first two starts, Mortensen (1-2) avoided giving up the big inning. While Minnesota's Denard Span hit a leadoff homer, Mortensen allowed only one more Minnesota player past second base.

''The other two games, he has been impressive and had one very bad inning,'' Oakland manager Bob Geren said. ''Tonight was an example of him not having that bad inning. It could have been early with the leadoff homer, but he rebounded and got out of that inning.''

Once he did, the Oakland offense took care of the rest. The five home runs was the most in a single game since hitting six homers at Arizona last June.

Cust hit the first of Oakland's homers - a massive shot to right-center that was estimated at 442 feet - to tie the game at 1 in the top of the second. The Athletics then broke the game open in the third off of Minnesota starter Nick Blackburn (9-11). Pennington led off with a solo home run before Rajai Davis doubled. Suzuki doubled in Davis and, after a Cust walk, Ellis hit a three-run homer to left to give Oakland a 6-1 lead.

That early deficit helped deal a blow to Minnesota's hopes of catching Detroit in the American League Central. Minnesota, which lost for the sixth time in nine games, could have pulled within 4 1/2 games after the Tigers lost at Toronto.

''Not a good night pitching-wise, I think we all saw we got hammered,'' said Minnesota manager Ron Gardenhire , whose team again fell below .500. ''They put balls in the seats. Blacky just couldn't make a pitch. I don't know how many homers he gave up. I don't know how many walks we had. I quit counting. Too many walks and too many hits. We get behind like that and it just got ugly.''

Blackburn is now 1-7 with a 7.36 ERA since the All-Star break. While he struggled, Minnesota relievers Bobby Keppel , Ron Mahay and Armando Gabino didn't fare much better.

Barton homered in the fifth and Suzuki homered in the sixth as Oakland opened a 12-1 lead. Ten of Oakland's 17 hits went for extra bases.

Francisco Liriano made his first appearance for the Twins since coming off of the disabled list, pitching two innings of scoreless relief while striking out four. Liriano, who was on the 2006 American League All-Star team, hadn't pitched since Aug. 17 because of left arm fatigue. It was Liriano's first appearance out of the bullpen since May 13, 2006. His previous 53 appearances had all been starts.

The Twins scored four runs on four in the bottom of the ninth.

NOTES: Oakland RHP Vin Mazzaro , who has tendinitis in his shoulder, threw from 140 feet before the game Friday. Athletics manager Bob Geren said the earliest Mazzaro could return to the mound is Thursday against Cleveland. ... Twins RH reliever Pat Neshek , who hasn't pitched since May 2008, has recovered from Tommy John ligament replacement surgery on his elbow and is throwing daily. He joined the team this week for a medical checkup and should be at full strength by spring training. ... The Twins will host St. Louis in a pair of exhibition games next April 2-3 to open the new Target Field. They are tentatively scheduled to host Boston in the first regular-season game on April 12, 2010.