The Red Sox’ David Ortiz watches his solo home run off Carlos Silva of the Twins during the sixth inning of last night’s game in Minneapolis.

AP / Jim Mone Jim Mone

MINNEAPOLIS — The vagaries of the knuckleball are well-documented, but one thing is fairly constant: Tim Wakefield’s signature pitch is somehow usually tougher to hit when thrown in a domed stadium.

Form held once again last night as Wakefield tossed seven shutout innings in the Metrodome against the Minnesota Twins. The Sox didn’t provide much in the way of offensive support, but David Ortiz’s upper-deck solo homer in the sixth and Coco Crisp’s run-scoring single in the ninth proved sufficient in providing a 2-0 win.

Wakefield improved to 7-3, 3.95 ERA in 11 career starts at the Metrodome.

The win was the third straight for the Red Sox, who added to their lead in the American League East. They now lead Toronto, Tampa and the Yankees by 6½ games, their largest at this stage of the season since 1946.

The victory was Boston’s seventh in the last eight road games and improved their road mark to 10-5, the best winning percentage (.667) in baseball away from home.

Wakefield allowed just three hits in his seven innings of work and evened his record at 3-3. In six starts this season, Wakefield has given up three runs or fewer in each start; in five of those starts, he has gone at least six innings.

The Twins didn’t collect a hit off him after the third inning as Wakefield retired 12 of the last 14 hitters he faced.

The Boston bullpen, which tossed four scoreless innings in relief of an ineffective Daisuke Matsuzaka Thursday night, had its challenges.

Former Twin J.C. Romero retired the first two hitters he faced in the eighth before Joe Mauer smacked an opposite-field double to put the potential tying run in scoring position.

But Brendan Donnelly got Torii Hunter to swing at the first pitch, resulting in a pop foul to first.

Jonathan Papelbon pitched the ninth for his ninth save in 10 opportunities.

Leading by a run in the ninth, the Sox got some breathing room when J.D. Drew drilled a leadoff triple to the gap in left-center and rode home one out later on Crisp’s sharp single to right. After a frightfully slow start, Crisp has now hit safely in nine of his last 10 games.

Blanked over the first five innings by Twins starter Carlos Silva, the Sox took a 1-0 lead in the sixth on Ortiz’s eighth homer of the season, a long wallop into the upper deck in right field. It served as one more painful reminder for the Twins that they never should have allowed Ortiz to get away after the 2002 season.

When Manny Ramirez followed up with a one-out double, the Sox had the opportunity to make it a big inning, but after Ramirez moved to third on a groundout by Drew, he was left there as Mike Lowell flied to left.

Alex Cora, getting another start at second, contributed his second triple of the week when right fielder Josh Rabe ran down a ball in the gap in right-center, only to have the ball clang off glove in a backhand attempt.

But once more, the Sox failed to capitalize as Julio Lugo flied to right.

The Sox managed just one baserunner in the first two innings, but had a chance to break through against Silva in the third.

Doug Mirabelli led off with a double and moved to third when Alex Cora dropped down a bunt to the right side of the infield for a sacrifice.

With the Twins infield playing in, Lugo hit a chopper over the mound that shortstop Jason Bartlett charged as Mirabelli broke for the plate. Bartletts throw was off line, but catcher Mike Redmond alertly turned in time to apply a swipe tag on the Red Sox catcher.

Wakefield had a pitch out of trouble in each of the first two frames, mostly due to control issues.

He plunked Mauer with one out in the first and when Hunter followed with a swinging bunt that rolled down the third base line, the Twins had two on and two out with Justin Morneau due.

But Wakefield got the 2006 A.L. MVP on a routine flyout to left, stranding two baserunners.

It was more of the same in the second. Jason Kubel worked a one-out walk and when Jason Bartlett doubled off the baggie in right, the Twins had two runners in scoring position.

Once more, however, Wakefield stiffened, getting infielder Luis Castillo on a soft liner to short to end the threat.

smcadam@projo.com