The move to slot Bolsinger in Sunday, coupled with Thursday's final off day of the regular season, allows the Dodgers to give Brett Anderson and Alex Wood an extra day of rest one more time through the rotation.
Anderson will start Monday in the series opener against the Diamondbacks.
"It's the extra day," Mattingly said. "It's the last time of the year to give it to [Anderson]."
Bolsinger is 6-3 with a 3.13 ERA in 18 starts for the Dodgers this season, with 85 strikeouts and 37 walks in 97⅔ innings. He owns a 119 ERA+, and with two more starts could join Zack Greinke (231), Clayton Kershaw (176) and Brett Anderson (112) as the first quartet of Dodgers pitchers with a 110 ERA+ and at least 20 starts since 1996.
Pirates ace Gerrit Cole will start the series finale for Pittsburgh on Sunday.
Bolsinger spent a month in the minors after the Dodgers acquired both Mat Latos and Alex Wood, despite having better numbers than both pitchers this season, albeit in fewer innings per start. Latos, 0-3 with a 6.66 ERA with the Dodgers, was designated for assignment on Thursday.
Would the Dodgers have been better off with Bolsinger in the rotation instead of Latos?
"You could always look back, and you could backseat drive all you want," Mattingly said. "But it just didn't work out."
Mattingly said he spoke with Latos after the loss on Tuesday to the Rockies, when Latos allowed the game-winning home run in the 16th inning.
"We talked to him the other day," Mattingly said. "He was frustrated from the standpoint that he wasn't pitching well, frustrated that he wasn't helping us. He handled it great."
Jimmy Rollins remains sidelined with a sprained right index finger that continues to bother him, but he was able to take grounders and make throws to first base during pregame drills. Rollins for now is available to pinch hit or pinch run.
Carl Crawford, who dealt with right hamstring tightness earlier in the week, is available to play now. "He's full go," said Mattingly.
Scott Van Slyke could be ready to return from his sore right hand on Saturday. "His hand is better today. We're hoping for tomorrow, but we'll see," Mattingly said. "He's a lot better but not quite there yet. We're being a little cautious with him."
Yasiel Puig did some running on Friday, in a straight line. He and Kiké Hernandez remain in the nebulous area of rehab without baseball activities. "They are still on the hamstring trail," said Mattingly.