BOSTON -- Jose Quintana started with five perfect innings. Conor Gillaspie hit a tying two-run homer in the ninth. The White Sox held the Red Sox to three hits.
Somehow, Boston still won 4-3 in 10 innings on Thursday.
"We had plenty of guys on base to knock in and we didn't do it," Chicago manager Robin Ventura said. "We had opportunities."
One of them came in the 10th when the White Sox had runners at first and second with one out. But the next two batters grounded out against Andrew Miller (3-5).
"They did better than we did at taking advantage of guys that were on base," Ventura said.
Boston drew two walks and David Ortiz hit a two-run double in the sixth when it scored three runs to take a 3-1 lead.
In the 10th, pinch-hitter Daniel Nava walked, Mookie Betts sacrificed him to second and Stephen Drew was walked intentionally. Then Mike Carp, hitting for David Ross, singled between shortstop and third base against Ronald Belisario (3-6) to give Boston its second consecutive walk-off win over Chicago.
In Boston's 5-4 comeback victory Wednesday night, Nava doubled in Betts for the tying run in the ninth and scored on Brock Holt's single.
Quintana "pitched a heck of a game," Chicago's Adam Eaton said Thursday. "Conor coming in, pinch-hit home run. He's been hotter than all get-out lately."
Carp spent more than a month on the disabled list with a fractured right foot. He watched the Red Sox struggle, knowing he could contribute.
Sometimes, he couldn't bear to look.
"Some of the nights, I almost had to turn the TV off in those situations because you can't be there to help," he said. "It's tough being on the DL with a boot on my foot."
The Red Sox, the defending World Series champions who are in last place in the AL East, ended their 3-7 homestand on a roll and head to Houston for a three-game series with a chance to build momentum going into the All-Star break.
"Hopefully it'll get us in a little bit of a rhythm, comfort level," said lefthander Jon Lester, who allowed one run and struck out 12 in seven innings.
Lester gave up seven hits and no walks. In his last six starts, he's 3-0 with a 1.01 ERA, 39 strikeouts, six walks and 33 hits allowed in 44⅔ innings. He extended his streak to 45 innings without giving up a homer.
But fellow All-Star Koji Uehara allowed Gillaspie's tying pinch-hit homer -- his third long ball in three games and fourth of the season.
Alexei Ramirez led off the ninth on Thursday with an infield single -- after first base umpire Cory Blaser's out call was reversed on replay. Uehara then struck out Paul Konerko before Gillaspie, batting for Moises Sierra, homered.
Lester trailed 1-0 after three batters. Eaton singled, Gordon Beckham struck out and Jose Abreu hit an RBI double over a leaping Jonny Gomes in left field. Lester then struck out Dayan Viciedo.
Lester fanned two batters in each of the first five innings and one each in the sixth and seventh before being replaced by Junichi Tazawa, who pitched a perfect eighth.
Boston went ahead in the sixth when the first three batters reached base on full counts.
"I really wanted to win this game because (Lester's) a really good pitcher," said Quintana, whose scoreless streak ended at 20⅔ innings, "but I had one bad inning in the sixth."
Drew became Boston's first runner with a walk and went to second on a walk to Ross. Jackie Bradley Jr. attempted to bunt on the first four pitches, then took a ball to bring the count to 3-2. He grounded a single to right field for Boston's first hit, driving in Drew with the tying run.
The next two batters were retired before Ortiz's double.
NOTES: Chicago lost its second straight game after winning its previous three. ... Boston scored in just five innings during the four-game series. ... Chicago LHP Chris Sale won the online fan vote for the final spot on the AL All-Star team, his third straight selection. "No matter, I think, how many you make, you still get excited about it," he said. ... The Red Sox send John Lackey (9-6) to the mound against Scott Feldman (4-5) in the opener of a three-game series at Houston on Friday night. The White Sox begin a three-game series at Cleveland with Hector Noesi (3-6) pitching against Corey Kluber (8-6) of the Indians.