Quick, name the most important player for the Red Sox after the All-Star break. “Clay, to me, is the biggest key for us in the second half,” manager John Farrell said. Fair enough. Clay Buchholz was 9-0 with a 1.71 ERA before suffering a shoulder injury that has prevented him from pitching since June 8. And although the ace right-hander has resumed throwing bullpen sessions, uncertainty regarding when he might return means the Sox must continue to monitor the trade market for starting pitchers. Just as critical, though, is the resurgence of left-hander Jon Lester, who enters the All-Star break with the sour taste of Saturday night’s 3-0 loss to the Oakland A’s but the consolation that he pitched far better than he has during the past few weeks. “Commanded pitches well, threw a lot of quality offspeed pitches, moved the fastball around. I think there’s a lot of positives,” Lester said. “Just pitch to pitch, everything was good, felt really good.” Indeed, Lester pitched well enough to win. But the Red Sox were shut out by A’s starter A.J. Griffin and closer Grant Balfour, leaving Lester no margin to make mistakes like the 0-2 fastball that Derek Norris hit for a solo homer in the fifth inning. Still, Lester yielded fewer than four runs for only the second time in seven starts.