Mike Cameron doubled twice, drove in two runs and scored three times for Boston. Jason Varitek added a solo homer.
The Red Sox, who are off on Memorial Day, went 18-11 in May after going 11-12 in April. Ortiz, who hit .143 with one homer and four RBIs in the first month of the season, batted .363 in May with 10 homers and 27 RBIs.
Lester (6-2) allowed one run and four hits to improve to 6-0 with a 1.43 ERA in his last seven starts.
The Red Sox scored three times in the fifth and sixth to take control. Ortiz’s two-run shot to center off reliever Brad Thompson (0-4) made it 4-1 in the fifth, and Cameron added a two-run double in the sixth.
Marco Scutaro had three hits and two RBIs for the Red Sox. His slow roller to the right of the mound in the fifth drove in Bill Hall and gave Boston a 2-1 lead.
Bruce Chen, inserted into Kansas City’s rotation when Gil Meche was placed on the 15-day disabled list Saturday with right shoulder bursitis, allowed one run and two hits in four innings. Thompson was tagged for six runs and seven hits in 1 2/3 innings.
Brayan Pena’s run-scoring grounder gave the Royals a 1-0 lead in the second. Ortiz’s sacrifice fly tied it in the third.
Notes
It was Cameron’s first two RBIs of the season. … Red Sox 2B Dustin Pedroia, hitless in his last 13 at-bats and just five for his last 40, was given the day off. Hall replaced him and batted eighth. … Chen pitched briefly with Boston in 2003, going 0-1 with a 5.11 ERA in five games. … Both teams had a different look, wearing white hats as part of baseball’s “Welcome Back Veterans” initiative. Red Sox manager Terry Francona joked “it looks like we’re selling ice cream.” … Kansas City’s David DeJesus went 0-for-4, ending his 11-game hitting streak. His bat slipped out of his hands during one plate appearance and went flying seven rows back, leading to a nice grab by a fan along the first-base line.