DETROIT — The managerial wheels were turning in the Boston Red Sox’ dugout.

It was clear to manager Terry Francona and pitching coach John Farrell that starter Julian Tavarez had lost his command. But they were just hoping that he could get through the fifth inning with the score still manageable from the point of view of the Sox, who were trailing at that moment by three runs.

But the Detroit Tigers didn’t cooperate. And Tavarez ultimately was to blame.

Francona had the Sox right-hander issue an intentional walk to Sean Casey, a left-handed hitter, with left-hander Javier Lopez warmed up in the bullpen. That loaded the bases with two outs.

Then Marcus Thames unloaded them, taking advantage of a mislocated 81-mph 1-and-2 fastball for a grand slam to left that put the Tigers on top, 8-1, en route to a 9-2 romp at Comerica Park last night.

“We were in a bind in that inning and it worked out as bad as it could have,” said Francona, who further explained his thinking in the situation.

“It was still just 4-1, so we’re trying not to get into our bullpen that early. If we go to Lopez there (to face Casey) and he gets Casey, then we’ve got to get through four innings from our bullpen,” said Francona, whose Sox are carrying only 11 pitchers, one less than usual, because of injury concerns to several everyday players.

“If (Lopez) doesn’t get Casey out there, then he’s facing a guy (Thames, a right-handed hitter) we don’t want him to have to face,” said Francona.

For a moment, it looked as if Francona was going to get his wish and have Tavarez set down Thames with his pitch count still in decent shape, which would have allowed him to start the sixth. The count went to 1 and 2 when Thames chased a down-and-away slider and missed it by several feet.

Tavarez and catcher Jason Varitek decided not to come back with the same pitch. Instead, Varitek called for a fastball inside. But Tavarez didn’t bury the pitch inside. Instead, Thames buried the pitch into the seats, expanding the Tigers’ lead from 4-1 to a game-over 8-1, especially the way rookie left-hander Andrew Miller (three hits, one run in seven innings) was pitching.

“When it went from 4-1 to 8-1, it was not a whole lot of fun from there,” said Francona.

Tavarez, meanwhile, knew even before his errant fastball met the wood of Thames’ bat that things weren’t going to go well for that pitch. He could see where it was heading.

“We go over scouting reports. I left it down and over the middle of the plate,” said Tavarez. “I could tell by the location. I made a mistake and it cost me. It cost the team. I let the team down tonight. I’m not making excuses. It was one of those things. I left a fastball over the plate. Little things hurt you.”

There were some members of the Sox who thought Tavarez might have been tipping his pitches. He wasn’t necessarily buying the theory.

“I’m not going to put that in my head. I just had a bad day,” said Tavarez.

The woeful start was one of the few this season by Tavarez, the team’s number five starter. It was the most runs he has allowed in a game this year, and it served to inflate his earned-run average from 4.39 to 4.97. Over his last three starts, including a 2-1 loss in his previous outing, Tavarez is 0-3 with a 7.36 ERA.

After authoring three scoreless inning, his command left him. Tavarez was nicked for three runs on four hits in the fourth and didn’t survive the fifth.

In addition to giving up 10 hits (including Curtis Granderson’s leadoff homer in the fifth) and one walk, Tavarez also hit two batters, the second of which, a plunking of Gary Sheffield in the fateful fifth, prompted plate umpire Jim Joyce to issue a warning to Tavarez, the Red Sox and the Tigers.

“When you hit a lefty (Mike Rebelo) and a righty (Sheffield), that’s a pretty good indication (there’s a lack of command),” said Francona. “When he’s struggling, he usually has one side of the plate to go to. But when you’re hitting guys on both sides, it’s quite a struggle.”

Earlier, some baserunning savvy by shortstop Julio Lugo paid off in giving Boston a 1-0 lead in the third.

Wily Mo Pena (triple) was thrown out at the plate by Granderson, the Tigers’ center fielder, trying to tag up and score on a fly ball hit by 28-year-old rookie Jeff Bailey.

“That was a tremendous throw, one of the better throws you’re going to see,” said Francona.

The Sox didn’t lose any life, though. Lugo drew a four-pitch walk. Miller then threw two straight balls to the next hitter, Coco Crisp, making it six straight out of the strike zone.

So with Miller’s concentration solely on the strike zone on his next pitch, Lugo got a tremendous jump and easily swiped second base. Crisp promptly cashed in Lugo with a single to center.

That, though, was the extent of the Sox’ offense against Miller. Doug Mirabelli, who replaced Varitek in the seventh, provided the Sox with their other run, leading off the ninth with a homer just inside the left-field foul pole off Chad Durbin, but the game was long gone by then for Boston.

skrasner@projo.com