John Lackey couldn’t fool himself yesterday, but he did fool more than a few future Tampa Bay Rays. Although many of the young kids who stepped into the batter’s box to face him left wondering what kind of pitch that was they’d just missed, Lackey couldn’t fool himself into thinking that facing a lineup of Tampa farmhands on an open-air field behind JetBlue Park was anything more than what it appeared to be, which is to say a slow day at the office. Yet it was another day in what has become an unbroken spring filled with them in his office, and that alone is reason for elation, an emotion Lackey didn’t often feel the past two years. When you haven’t thrown in competitive earnest since Sept. 25, 2011, you’ll take your elation where you find it, even if it’s on a minor league field against kids barely ready to shave. “Pitching on the backfield on an off day (for his teammates), motivation is an issue,” Lackey joked, “but I got to the number of pitches I wanted. I got up six times. I got my work in.’’ That was the right way to look at things for a guy who has suffered through two years with a sore elbow, painful personal problems and an $84 million contract he couldn’t possibly do enough to justify in the state he was in both physically and mentally. Now those troubles are behind him and, as he showed again yesterday, so too is the surliness that so often punctuated his every public appearance. It has been replaced by an affability often talked about by his teammates but infrequently seen outside the closed doors of the clubhouse since his arrival in Boston three-plus years and one surgery ago. It is difficult to know which transplant will be more important for Lackey and the Red Sox this summer — his new public persona or his new elbow. Important as it is to Sox management that the dark days of the recent past be replaced by sunshiny affability, the latter would seem to be more significant, although perhaps also the more difficult to rebuild. First performed in 1974 by Dr. Frank Jobe, the reconstruction of the ulnar collateral ligament in the elbow was once seen as radical surgery but now is so familiar among baseball players that it is thought of and written about in some circles as if a guy just had his tonsils removed. Lackey seemed to gently try to remind the world of that when someone asked if the 93-mph fastball he registered on the radar gun yesterday could be improved upon. “I hope so, especially (when it’s) on a back field on an off day,” he said. “But anybody who has surgery has some doubts when they start throwing (again). I got a big zipper on my arm for a reason.”