BOSTON (AP) – Jon Lester struck out 10 in six innings in his third major league game, David Ortiz hit a grand slam and the Boston Red Sox won their sixth straight, 9-3 over the Washington Nationals on Wednesday night.

Lester, Boston’s top pitching prospect when he joined the team on June 10, allowed three hits and two walks. He finished his night by striking out Matthew LeCroy on a 92 mph fastball. The left-hander pumped his fist before walking toward the dugout to a standing ovation.

Lester (2-0) had the most strikeouts by a Red Sox pitcher this season – Curt Schilling and Tim Wakefield each had nine in a game – and the most by a Boston rookie since Casey Fossum also had 10 against Cleveland on Sept. 18, 2002.

Ortiz hit his 21st homer of the season and fifth career grand slam to give Boston a 4-0 lead in the second as he increased his AL-leading RBI total to 64. The homer came against rookie right-hander Shawn Hill (1-2) as Boston completed a three-game sweep.

The Red Sox outscored the Nationals 26-9 and out-hit them 46-22 in the series. Boston scored four runs in both the second and sixth innings, all with two outs.

Washington lost for the eighth time in 10 games with the only wins coming in its last at-bat last Saturday and Sunday against the New York Yankees.

With starters Matt Clement, David Wells and Lenny DiNardo on the disabled list, Lester has filled a major void in the rotation after appearing in just 11 games at Triple-A before being called up from Pawtucket.

He allowed his only run in the third inning on a double by Damian Jackson and an RBI single by Alfonso Soriano that was a bloop over the head of first baseman Kevin Youkilis.

The Red Sox made it 5-1 in the fifth when Trot Nixon doubled, took third on Jason Varitek’s single and scored on Mike Lowell’s double-play grounder.

They added four runs in the sixth after Alex Gonzalez led off with a double. He took third on Mark Loretta’s grounder for the second out. Ortiz was walked intentionally and Manny Ramirez singled in Gonzalez.

Mike Stanton replaced Hill and allowed a two-run double to Nixon and an RBI double to Varitek that made it 9-1.

Washington scored a run in the seventh on Robert Fick’s RBI single and added another in the ninth on Jackson’s RBI single.

Notes: Ortiz is one of three players in major league history to hit all five of his grand slams in the same park. Cecil Cooper did it at County Stadium in Milwaukee and Ken Williams did it in Sportsman’s Park in St. Louis. … Boston improved to 8-1 in interleague play, winning its sixth in a row against NL teams. … The Red Sox are 9-2 in their last 11 games at Fenway Park. … Boston played its 10th straight errorless game, its longest streak since Sept. 26 to Oct. 5, 1986. … The Nationals/Montreal Expos franchise is 0-9 at Fenway. … Washington pitchers have allowed at least 10 hits in 10 of the last 13 games.

AP-ES-06-21-06 2205EDT