"I don't think all the blame should be on Kenley. The game should have been over a couple times in that inning," Roberts said after L.A.'s 5-3 loss -- and Jansen's third consecutive blown save.
The Giants trailed 3-1 going into the ninth inning. San Francisco's Jason Vosler got a good lead off first base with the bases loaded and beat Dodgers shortstop Chris Taylor's throw to second on an infield single by Thairo Estrada. That kept the game going and scored Wilmer Flores to bring San Francisco to 3-2.
Vosler was initially ruled out at second for the final out, but the call was overturned following a replay review.
Darin Ruf then checked his swing on a full-count cutter -- although replays appeared to show he went around -- to draw a walk from Jansen that forced in the tying run.
Roberts yanked off his cap and argued vehemently, leading to him being ejected in the ninth inning for the second consecutive night.
"There's no doubt in my mind that he went and the game should have been over. In that spot with two contending teams, you just can't miss that call," Roberts said. "We should have won that game, and it's a game we really wanted, we had, and we didn't."
LaMonte Wade Jr. then hit a sinking liner to right field for two-run single, giving San Francisco a 5-3 advantage.
Jansen was lifted to a chorus of boos for the second straight night. On Wednesday, he served up the go-ahead home run to Flores in the Dodgers' 4-2 loss.
Jansen (1-4) fell to 21 for 26 in save opportunities this season. He has allowed seven runs on seven hits with four walks in one inning over the past two games.
He has compiled 333 regular-season saves in 12 years with the Dodgers but has drawn the ire of fans over a string of inconsistent performances during the past three years, most notably in the postseason. The 33-year-old right-hander appeared to return to prime form in 2021, posting a 1.24 ERA while converting 21 of 23 save chances through his first 36 appearances. But he blew a one-run lead against the Colorado Rockies on Sunday, followed by the two Giants rallies.
ESPN's Alden Gonzalez and The Associated Press contributed to this report.