BOSTON -- John Lackey allowed one run in six sharp innings in just his second start since 2011, Stephen Drew broke open a tie game in the fourth inning with a two-run triple and the sizzling Boston Red Sox kept on rolling with a 6-1 victory over the Houston Astros on Sunday.
Dustin Pedroia, Mike Carp and David Ortiz had RBI doubles for Boston, which won its fifth straight game and for the 15th time in its last 20 to improve to 18-7, the best mark in baseball. The 18 victories ties a club record for wins in April, established in 1998 and matched in 2003.
It also was the Red Sox's third series sweep this season, tying the team's total for all of last year, and first in a four-game set since July 2011.
Perhaps even more impressive than its starting pitching, which improved to 15-4 this season, is Boston's bats. The Red Sox exploded for 11 more hits Sunday and smacked 51 in the series.
Ortiz went 2 for 4 with an RBI single in the first, extending his hitting streak to 20 games dating to July 2, 2012, the longest of his 17-year career.
Despite missing 71 of the final 72 games last season and all of spring training with a heel injury, the 37-year-old Ortiz is hitting .516 (16 for 31) with five doubles, two home runs and 11 RBI in eight games since returning to the lineup on April 20.
The Astros, meanwhile, continue to struggle in their first season in the American League after the franchise's first 51 years in the National League. They've lost seven of their last nine games and 12 of 15 overall to fall to 7-18, the worst record in the AL and second worst in the majors.
Lackey (1-1) missed the 2012 season after undergoing successful Tommy John surgery to reconstruct a torn ulnar collateral ligament in his right arm. He returned to the rotation for the first time Sunday since April 6 when he left the game with a right biceps strain that landed him on the disabled list.
His right arm looked just fine Sunday.
Lackey yielded five hits with two walks and four strikeouts to pick up his first win since Sept. 25, 2011, against the New York Yankees. Three relievers then combined on one-hit ball in the final three innings.
After allowing a run in the first inning, Lackey retired 14 of the next 15 batters he faced, including 12 straight, until Jason Castro singled with one out in the sixth. Carlos Pena and Ronny Cedeno followed with one-out singles to load the bases, but Lackey pitched out of peril, striking out Fernando Martinez and inducing Matt Dominguez to ground out on one pitch.
Bud Norris (3-3) was making his first career start at Fenway Park, and it wasn't quite as memorable.
The right-hander surrendered five runs -- three earned -- and nine hits with two walks and six strikeouts in six innings.
Ortiz knotted the score with an RBI single in the first before Boston busted it open in the fourth, taking the lead for good when Carp and Jarrod Saltalamachia reached on consecutive singles and scored on Drew's triple to the right-field corner.
Pedroia and Carp stretched the lead to 5-1 with run-scoring doubles to left field in the fifth, and Ortiz followed with an RBI double down the right-field line in the seventh.
After getting two quick outs to begin the game, Lackey walked back-to-back batters before Cedeno delivered an RBI single up the middle for a 1-0 lead. Dominguez led off the second with a single, but that was it for Houston until the sixth.
NOTES: The Red Sox closed a 10-game homestand, their longest of the season, with a 7-3 record. ... Boston has been in first place or tied for first all 28 days of the season, marking the longest continuous stretch that a Red Sox team has maintained first place to begin a season. The previous record was the first 25 days of the 1918 season. ... The Astros fell to 0-7 all time at Fenway Park and 2-11 against the Red Sox overall. ... Houston shortstop Marwin Gonzalez made two errors on one play in the bottom of the fifth. The first came on a grounder by Daniel Nava that Gonzalez failed to field cleanly, and he followed that with a wild throw to first that landed in the first row of seats directly behind Boston's dugout. ... Nava made a spectacular diving catch in right field to end the game.