But for Ortiz, the award is testimony to his rise above a miserable and frustrating April that had put the remainder of his career under a microscope.
Being a good teammate, Lester sounded more gratified by the recognition for Ortiz.
"[Ortiz] deserves it. It was a huge month for him, not only for us as a team, but personally," Lester said. "I think a lot of people wrote him off at the beginning of the year. He kind of came back and stuck it in their face and said, 'I'm not going anywhere.' It's good to see him be a presence in our lineup again and a presence in our clubhouse. With him swinging the bat like that and having that attitude he's always had, it helps this clubhouse out."
Coming off an opening month during which he had batted .143 and drove in only four runs while striking out 21 times in 56 at-bats, Big Papi lit up May with a .363 average that included 10 homers and 27 RBIs.
Ortiz's .788 slugging percentage and .424 on-base percentage both were Major League highs for the month.
The monthly award is the fourth for Ortiz, who was last cited in September 2007.
Lester's month was highlighted by the May 20 complete-game victory against the Twins in which he struck out nine without issuing a walk -- the first Boston pitcher to whiff as many without a base on balls since Pedro Martinez did it six years ago.
"He was awesome," Ortiz said of Lester. "He's been pitching his [butt] off. Like I said, we're going to try to continue it, because it makes a huge difference, him pitching like that and me hitting the way I was -- of course, with the support of all our teammates and fans. It's a good thing."
Lester, whose lifetime .727 (48-18) winning percentage is the best in Major League history among pitchers with 50-plus decisions, last earned Pitcher of the Month honors in September 2008 and has received the award a total of three times.
"That's stuff you don't really play for, but it's nice," said Lester. "I'm obviously honored to be named that. But I'm just more concerned with how our team's been playing. We've been playing better baseball."
The Red Sox went 18-11 after entering May with a losing (11-12) record.
"It tells me that when I get it going, good things happen," Ortiz said of the mutual resurgence. "It's good stuff. I'll try to continue doing that and try to get a few more [monthly awards]."
Texas DH Vladimir Guerrero, who batted .330 with an Ortiz-matching 10 homers while leading the Majors with 31 RBIs, was runner-up for Player of the Month honors.
Finishing second in the Pitcher of the Month vote was Toronto right-hander Shaun Marcum, who also went 5-0 and posted an ERA of 1.85.