BOSTON — Kansas City's Billy Butler summed up Jon Lester's performance, paused for a few seconds, and realized it was a lost weekend for the Royals.
Lester allowed no earned runs for the third time in four starts, and the Boston Red Sox completed a three-game sweep of the Royals with a 6-0 win Sunday.
"That was probably the best stuff he's had all year," Butler said. "It was their day — their weekend."
One day after getting held to one run, the Royals were blanked for the eighth time this season. They have scored one run or none in four of their last six games.
"On a day like today, the only thing you can do is hope Jon Lester doesn't bring his A-game, and he gets his pitch count up and makes mistakes, and you take advantage of it," Royals manager Ned Yost said. "He was pretty good."
Kansas City lost for the ninth time in 12 games and fell to 9-17 since a 10-game winning streak. The Royals have another tough matchup on Monday night when they open a three-game series against another All-Star lefty — Chris Sale of the Chicago White Sox.
"You basically just shake it off and get right back out there," Butler said. "We faced a tough left-hander today and it doesn't get any easier."
Yordano Ventura (7-8) gave up all six runs.
"Mostly command," Yost said. "Just struggled with command a little. He got some pitches in the fat part of the strike zone."
In eight innings, Lester struck out eight and gave up two walks and four hits. Only one Royals player reached third base.
Lester (10-7) is 4-0 with a 0.85 ERA over his last seven starts with 47 strikeouts and eight walks in a span of 52 2-3 innings. He has yielded just one earned run in 31 innings.
Lester extended his scoreless streak to 14 innings before Junichi Tazawa got the first out of the ninth. Edward Mujica retired the next two batters.
The first scored on Dustin Pedroia's forceout at second base in the first, Daniel Nava hit a two-run double in the third, and Boston added three in the fourth on David Ross' two-run homer and Nava's sacrifice fly.
That was more than enough support for Lester as he keeps building a case for a lucrative contract following the one that expires after this season.
Boston entered the game in last place in the AL East, percentage points behind Tampa Bay, but won for the seventh time in eight games.
The Royals put runners at first and second in the first when Eric Hosmer was hit by a pitch with two outs, and Danny Valencia singled. But Alex Gordon flied to left.
Alcides Escobar was left on base after a one-out single in the second, and Lester retired eight consecutive batters before Escobar led off the fifth with a double. He reached third on a one-out groundout, but the threat ended when Lorenzo Cain flied out, leaving him hitless in 22 at bats.
Hosmer singled with one out in the sixth to extend his hitting streak to 16 games. After Valencia struck out, Gordon drew a walk, the first issued by Lester in three starts. But Butler grounded out.
Cain walked leading off the eighth, but Lester finished his outing by getting Omar Infante to ground into a double play before fanning Hosmer.
Brock Holt scored Boston's first run after he and Nava singled. Nava's double in the third came after a walk to Ross and a single by Jackie Bradley Jr. In the fourth, Shane Victorino doubled and scored on Ross' sixth homer. Nava's sacrifice fly drove in Bradley, who had singled.