The younger Yastrzemski was hitting .316 (43 for 136) with 12 home runs and 25 RBIs in 40 games with Triple-A Sacramento. He is playing left field and batting seventh against the Diamondbacks.
The 28-year-old Yastrzemski was originally drafted by the Baltimore Orioles in 2013 and played 703 games with 2,600 at-bats in the minors. San Francisco traded for him in March, a deal that sent minor league right-hander Tyler Herb to the Orioles.
Mac Willamson was designated for assignment to make room for Yastrzemski. Williamson struck out five times in five at-bats against Atlanta on Thursday, then whiffed three more times in the series opener against Arizona on Friday.
The Giants also placed reliever Trevor Gott on the 10-day injured list with a right forearm strain and recalled right-hander Dereck Rodríguez from Sacramento.
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