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BOSTON -- John Lackey can appreciate his teammates' offense even more with the struggles he's gone through this season.

David Ortiz hit a grand slam to cap a five-run fourth inning and Dustin Pedroia extended his career-best hitting streak to 24 games with a solo homer, carrying the Boston Red Sox to another big offensive night with a 12-5 win over the Kansas City Royals on Wednesday.

Jacoby Ellsbury homered leading off the first inning and Pedroia followed with his homer for the Red Sox, who won for the 19th time in 23 games and scored in double digits for the second straight game.

"That's one of the reasons I came here," Lackey said when asked what it's like watching the top of Boston's offense -- mainly Ellsbury and Pedroia -- hitting the way they are recently. "I didn't get a lot of that in Anaheim. Jacoby's having a great season, he's getting a little of everything and (Pedroia) is on fire."

Pedroia, who went 4-for-5 in Tuesday's 13-9 win, added two singles and a sacrifice fly, Ellsbury had three hits to increase his average to .325 and Adrian Gonzalez had three hits and three RBIs to raise his major league-leading total to 87.

Lackey (9-8) won his fourth straight start, allowing four runs -- three earned -- and 11 hits, walking one and striking out three in 5 2/3 innings. Before the current run, his ERA was 7.47 and he was the object of the fans' ire during rough starts.

But he's turned it around and the offense has been there for him, too, scoring six and seven runs, respectively, in his previous two starts.

"I don't think anybody would complain about sitting around and watching guys score runs," he said.

Eric Hosmer hit a three-run homer and Billy Butler added a solo shot for the Royals.

Like Tuesday's loss, Kansas City blew an early lead. After Hosmer's homer put the Royals up 3-0 in the first, Boston scored two runs in the bottom of the inning and three in the second before breaking it open in the fourth against starter Bruce Chen (5-4).

Boston had 16 hits, reaching double digits for the 11th straight home game.

It was the first time Boston's first two batters homered since July 21, 1995.

Ellsbury's caromed off the Pesky Pole in right and Pedroia hit his into the Green Monster seats, extending his career-best streak, the longest by a second baseman in club history.

"We started out in the game and we're down 3-0 and that's not an easy way to play," Boston manager Terry Francona said. "We get the two home runs and 'OK, we're right back.'"

In the second, Ellsbury drew a bases-loaded walk, Pedroia had a sacrifice fly and Gonzalez's run-scoring grounder made it 5-3.

The Red Sox broke it open with the five-run fourth that was highlighted by Ortiz's slam. Pedroia, Gonzalez and Kevin Youkilis singled before Ortiz belted his 10th career slam -- ninth with the Red Sox -- over Boston's bullpen, tying him with Rico Petrocelli for second all-time in club history behind Ted Williams' 17. Yamaico Navarro had an RBI single earlier in the inning.

"A pitcher would rather walk you than make a mistake that leads to four runs," Ortiz said. "You have to be ready for (a mistake)."

And he certainly looked like he was.

"We were still in that game, but when Papi hit that home run, it kind of took the life out of us," Royals right fielder Jeff Francoeur said. "That's what he does."

With the slam, Ortiz reached 1,000 RBIs with Boston.

Chen was tagged for 10 runs and 10 hits in four innings, throwing 114 pitches in his brief outing.

"He wasn't anywhere near as sharp," Royals manager Ned Yost said. "He really struggled to command the strike zone, had 114 pitches after four innings and just couldn't command the ball and throw it where he wanted to. Bruce is usually pretty good at doing that."

Bulter's homer made it 10-4 in the fifth.

Game notes

Pedroia's hitting streak is the AL's longest this season. He broke a tie with Del Pratt's 23-gamer in 1922. ... Gordon had a career-high three doubles. ... Red Sox 3B Youkilis, who missed Tuesday's game with a strained right hamstring, was not in the original lineup but came in and told Francona he felt fine. "He came in and said 'There's no reason for me not to play,'" Francona said. ... Hosmer came into the game 15-for-30 in the past seven. ... Boston third-base coach Tim Bogar was hit in the back of the helmet by Pedroia's foul liner in the second, sending the helmet flying, but he put it back on, smiled and didn't need to be checked out on the field. ... Chen had allowed one run or less in three of his five starts since coming off the DL on June 24. ... Francona rested struggling LF Carl Crawford with the lefty Chen starting. "It was a good night," the manager said. "He hasn't had much success against this guy." Crawford was 1-for-11 in the first two games of the series, 0-for-6 with four strikeouts Monday. ... The Royals blew three leads in Tuesday's loss.