SAN FRANCISCO — Zack Wheeler was back on a mound Friday, if only for 13 pitches.

The Mets right-hander, who is recovering from a shoulder impingement, played catch for a third straight day and then took to a bullpen mound, where he threw from the slope.

He will need to throw a full bullpen session before he is considered for removal from the injured list, but manager Mickey Callaway wouldn’t rule out the possibility Wheeler might be ready for the team’s next series, against the Padres, upon returning to Citi Field on Tuesday.

The calendar is an issue if the Mets intend to deal Wheeler by the July 31 trade deadline. If Wheeler can return by Thursday, he would potentially have two starts to show interested teams he is healthy.

In need of bullpen arms following their 3-2 loss in 16 innings Thursday, the Mets recalled Stephen Nogosek and Tyler Bashlor from Triple-A Syracuse. Chris Mazza and Luis Guillorme were optioned to create roster space.

Mazza was the losing pitcher in the marathon, surrendering two runs without recording an out in his second inning of work. The right-hander had thrown 34 pitches the previous day.

The Mets will have to make another roster move Saturday, when Walker Lockett is recalled from Syracuse to start against the Giants.

Jacob Rhame was available from the bullpen Friday, after serving a one-game suspension the previous day, and could be optioned to create space for Lockett.

Callaway credited the return of Noah Syndergaard’s slider for the right-hander’s strong performance against the Giants on Thursday. Syndergaard, who has struggled for much of the season to get a feel for his slider, allowed one run over seven innings.

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“It’s location and confidence,” Callaway said. “And the location probably comes because of the confidence.”

Jacob deGrom entered his Friday start needing five strikeouts to surpass Ron Darling for sixth place on the franchise’s all-time strikeout list. Darling had 1,148 strikeouts during his Mets career. Fifth on the Mets’ all-time list is David Cone, who struck out 1,172 for the team.

The Mets’ bullpen entered play 1-1 with a 2.16 ERA in six games since the All-Star break. In the first half, the Mets bullpen pitched to a 5.30 ERA.

“Probably the biggest factor is they have been working hard on adjustments and I feel like they are making them,” Callaway said.