The Giants recalled Misch and sent struggling right-handed reliever Osiris Matos to Fresno.
"He's been throwing the ball well," Giants manager Bruce Bochy said of Misch before Tuesday's game against the Nationals. "He's been locating his fastball, throwing strikes. He's a guy who can provide long relief for us. He's been up here, he's got experience.
"It's good to see him get untracked and throw the ball the way he's been throwing down there. We've had good reports on him. That's why he's up here."
In 11 relief appearances with the Grizzlies, Misch was 2-0 with a 2.45 ERA and one save. He held opponents to a .272 average (22-for-87).
"I feel great," Misch said. "I love getting the ball. The last month, month and a half, I've been taking the ball every week. I'm just trying to pump the zone."
Misch heard the good news late Monday night while riding the team bus from Reno to Fresno. By the time he arrived at his Fresno home, it was 6:30 a.m.
"Couple hours sleep, packed some stuff, took a flight and here I am," said Misch, who arrived at the clubhouse shortly before 6 p.m. PT.
Misch appeared in 15 games last season for the Giants, including seven starts. He was 0-3 with a 5.68 ERA. Overall, he's 0-7 with a 5.00 ERA in the Majors.
"Really, the way we are right now, we need a fresh arm," Bochy said. "We have been using [Justin] Miller a lot, Matos a lot. We ended up having to get some guys up, having to go extra innings in L.A. Another guy to help provide relief and give us some innings at this point, especially a long guy.
"If something happened, we could leave him out there and he could go three, four or five innings. Really, the other guys aren't prepared to do that where Patrick is."
Matos had an ERA of 9.00 in five appearances, allowing 11 hits and six earned runs in six innings. On Monday night against Washington, he gave up four hits and three earned runs in 1 2/3 innings. That came on the heels of Saturday's appearance against the Dodgers in which he gave up four hits and two earned runs in one inning.
Eric Gilmore is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.