Bart’s arrival means breather for Casali

With the luxury of essentially a free roster spot this weekend, the Giants used it to activate one of their top prospects, catcher Joey Bart, who was in the lineup for the first time this season Saturday against Nationals lefthander Jon Lester.

“I’m really excited,” said Bart, who had two hits, drove in a run and scored another. “I’m glad they called on me — whether it’s today or tomorrow or however long, I’m going to come out full speed ahead.”

The team does not need a fifth starter until July 20, and Logan Webb, who came off the injured list for a strong threeinning outing Friday, needs to get in work, so he was sent to TripleA Sacramento. Webb will be an option for the Giants’ postAllStar break rotation, said manager Gabe Kapler.

Bart, 24, is the Giants’ No. 2 prospect, according to Baseball America, and, among other things, Saturday’s game might allow the team to showcase Bart should the Giants dangle him as part of a trade package with the deadline in three weeks.

The No. 2 pick in the 2018 draft, Bart made his bigleague debut last season after AllStar catcher Buster Posey opted out of the shortened season. Bart did not appear ready, batting .231 with zero homers and seven RBIs in 33 games. He threw out just five of 28 attempted base stealers.

That experience still proved valuable; Bart has worked hard to improve in all areas, and team president of baseball operations Farhan Zaidi said, “The atbat quality has been better, he’s been really consistent, and really good defensively as well, so we’re really happy with his progress.”

“I feel like I’ve improved offensively and defensively, I’m just trying to be a more complete player,” Bart said. “I just want to swing at better pitches and try to frame the ball better on the defensive side.”

Bart had not worked a lot with Saturday’s starter, Anthony DeSclafani, though he had caught him in the bullpen.

For Kapler, Saturday’s move meant he could give Curt Casali a full day off. Like many veteran backup catchers, Casali tends to be less effective with overuse. He also has had some back stiffness, but he’s been doing double duty with Posey out with a thumb injury.

“We sort of ran into a stretch where he played three days in a row, and I don’t think it was especially kind on his body, so I just want to make sure that we get him days off the same way we would Buster,” Kapler said. “I think Curt deserves the same level of respect as any of our other players and I think what is best is to give him this blow.

“It’s also a nice opportunity for Joey to step up and help this team. I think he’s been waiting for this opportunity for a long time and he’s very well prepared for it.”

Briefly: Outfielder Mike Tauchman (knee) started a rehab assignment with TripleA Sacramento . ... The Giants have the 14th pick in the first round of the MLB draft, which begins at 4 p.m. Sunday.