DENVER — The Red Sox reconfigured their rotation for a two-game interleague series against the Colorado Rockies, deciding to pitch John Lackey Tuesday night rather than give him some extra time off.
The Sox wrapped up the American League East title last week but are intent on having the best record in the league and home-field advantage throughout the postseason.
But Lackey looked like a pitcher in need of a rest. He allowed three home runs, and poor relief pitching followed as the Rockies beat the Red Sox, 8-3.
Tyler Chatwood (8-5) and two relievers held the Sox to seven hits.
Given the circumstances and the competition, it was a poor effort by the Red Sox. The Rockies (72-86) are one of the worst teams in the National League and were 4-14 in interleague games this season.
The Sox were trailing, 8-1, until Jarrod Saltalamacchia’s two-run homer in the ninth inning.
Lackey (10-13) allowed four runs on six hits over six innings. The three home runs matched his most in a game this season. Lackey walked one and struck out five.
Lackey came in with a career 17-9 record and 3.08 earned run average in interleague games. In four starts this season against NL teams, he had a 2.48 ERA. That included holding the Rockies to two runs over seven innings at Fenway Park on June 26 in a game the Red Sox won.
But Lackey was not as sharp Tuesday night.
Charlie Blackmon led off the bottom of the first inning with a home run to right field, his sixth of the season. With two outs, Michael Cuddyer lined a ball to right field that backed Shane Victorino up to the warning track. He had a play on the ball but it ticked off his glove for a double.
Todd Helton, who is retiring after 17 seasons and will play his final home game Wednesday, ripped the next pitch into left field for an RBI single.
Troy Tulowitzki (third inning to center) and Corey Dickerson (fourth inning to right) had solo home runs as the Rockies took a 4-0 lead.
Chatwood was working on a two-hit shutout with two outs in the seventh inning when Will Middlebrooks doubled to right field, the ball eluding the leap of Cuddyer.
Jackie Bradley Jr. followed with a hard-hit grounder to first base that Helton stopped with a dive. His flip to Chatwood was accurate but the pitcher dropped the ball.
Middlebrooks, running hard with two outs, headed for the plate. Chatwood then committed a second error by throwing the ball into the Red Sox dugout.
Bradley was awarded third on the error. Mike Carp pinch hit for Lackey. The 2-and-2 pitch from Chatwood got by catcher Jordan Pacheco and Bradley broke for the plate.
The ball caromed hard off the backstop, right back to the catcher. Pacheco got the ball to Chatwood and Bradley was out to end the inning.
Trailing, 4-1, the Sox started the bottom of the inning with rookie lefthander Drake Britton on the mound. Pacheco doubled to left field.
In came rookie righthander Brandon Workman for his first appearance in a week. He let the game get out of hand.
Pinch hitter Josh Rutledge singled to right before Workman walked Blackmon to load the base.
D.J. Le Mahieu followed with a two-run single to center. After an uncontested double steal, Cuddyer had a broken-bat two-run single to right and the Sox were trailing, 8-1.
Franklin Morales, who started his career with the Rockies, came in and ended the inning without further damage. But the Rockies sent nine batters to the plate and four scored.
Given what is at stake, it was a surprisingly poor effort by the Sox.
They started the night with a one-game lead on Oakland for the best record in the American League. The benefits of that status are significant.
The top seed will face the winner of the one-game wild-card playoff game Oct. 2. The alternative is facing the Detroit Tigers, the likely No. 3 seed.
The top seed also gets home-field advantage throughout the postseason.
“By the way we play at home and the way our guys embrace our environment, it would be a very good thing,” Sox manager John Farrell said before the game.
If the Sox and Athletics finish in a tie, the tiebreakers go to Oakland.
The teams split six games this season, eliminating the first tiebreaker. The second tiebreaker is intradivision play, which again is likely to end up with a tie if the teams tie.
The third tiebreaker would be overall intraleague record. That also is likely to be tied if the teams have the same record.
The fourth tiebreaker, and the deciding one, would be the second-half intraleague record. The A’s, through Monday, were 42-24 and the Sox 39-29.
Farrell hopes it doesn’t come to that.
“We’re also in a position where we control our own destiny,” he said. “The rules are the rules. The schedule is not going to be fair to everybody.”