Cincinnati lost its fifth straight game and has scored five runs with 18 hits during the skid, which dropped it 2 1/2 games behind NL Central-leading Milwaukee.
Wilmer Flores had two doubles and a home run for San Francisco, which improved to 17-7 against the NL Central.
The score was tied 2-2 Monday night when the game was suspended with one out in the top of the eighth after a wait of 1 hour, 55 minutes.
With automatic runner Brett Wisely on second, Pederson drove a pitch from Ian Gibaut (8-2) that hit the left-field wall on a hop. Pederson advanced on Flores' groundout and scored when, with the infield in, Michael Conforto hit a sharp grounder to a diving Jonathan India. Pederson scored standing up ahead of an off-line throw from the second baseman.
Reds rookie Elly De La Cruz, in a 1-for-19 slide, had walked leading off the ninth against Tyler Rogers (3-4). De La Cruz stole his 17th base - he was initially being called out by second base umpire Adam Beck but the decision was reversed in a video review.
Before the next pitch, Rogers picked off De La Cruz, who tried for third and was caught stealing for the third time this year.
“Selling that inside move is a huge emphasis for us," manager Gabe Kapler said. "It was great to see it all come together. It won the game for us. It’s tough to execute for all pitchers. Tyler did a nice job setting it up. He’s one of the fastest players in the game. You want to keep him where he is and not let him get to third. Erasing the baserunner may have been the most important moment of the game.”
De La Cruz led off for the first time after batting cleanup in his first 33 starts.
“Elly had a great at-bat and great stolen base," Reds manager David Bell said. "He got picked off. We learn from that. I’m very proud of how our players, how hard they’re working. We will continue to take that same approach. No matter what happens on the field we’ll move forward. There’s no other choice.mYou have to stay aggressive. You can’t be fearful.”
Camilo Doval struck out two in a 1-2-3 10th for his 29th save in 31 chances, finishing a four-hitter.
On Monday, Austin Slater and Flores homered off Brandon Williamson. Matt McLain and India homered against Logan Webb.
Right-hander Luke Weaver (2-2) was to start the scheduled game for Cincinnati and right-hander Anthony DeSclafani (4-8) for San Francisco.
Christian Encarnacion-Strand, a top 23-year-old Reds prospect, was 0 for 3 as a designated hitter in his major league debut. According to Major League Baseball, at 27 characters his name is the longest in big league history, five longer than Minnesota pitcher Simeon Woods Richardson. MLB included the hyphen in its count.
The Reds added RHP Tony Santillan as their 27th man for Tuesday's second game. The Giants added switch-hitting OF Bryce Johnson.
Giants: Manager Gabe Kapler expects RHP Luke Jackson (low back strain) to join the team on the current trip after he threw 18 pitches in his second Arizona rehab assignment on Monday.
Reds: The returns of RHP Hunter Greene (right hip) and LHP Nick Lodolo (left calf tendinosis), two recent No. 1 draft picks for Cincinnati, both remain open-ended. Lodolo, the 2019 top choice, is rehabbing in Cincinnati. Greene, the 2017 pick, is working in Goodyear, Arizona.
Giants RHP Ross Stripling (0-2) is scheduled to start on Wednesday against RHP Graham Ashcraft(4-7).
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