Castellanos also homered and singled to help Cincinnati improve to 7-2 in extra-inning games this season. Lucas Sims (3-1) pitched two innings for the win.
Jesse Winkler was at second base to start the 12th and Castellanos hit a pitch from Antonio Santos (0-1) to the wall to make it 5-4. Pinch-hitter Nick Senzel singled and Eugenio Suarez had an RBI groundout.
Colorado got a run on Raimel Tapia’s groundout in the bottom of the inning off Heath Hembree, who earned his first save.
The Reds have played the most extra-inning games in the majors.
“Extra innings, everybody’s up, everybody’s believing in the guy that they’re going to get it done,” Castellanos said of the team’s success.
“It felt really good. It was great,” Farmer said of his third home run of the season. “I’ve come close a couple of times. I didn’t think I had any more power left in me.”
The teams combined for 36 runs in the first two games, and early it looked like another big scoring night.
Ryan McMahon hit his ninth homer, a 478-foot shot according to Statcast, to put the Rockies ahead 2-0 in the first. Castellanos responded with a two-run shot in the third off Jhoulys Chacín, his 10th.
The pitching took over from there. Cincinnati starter Tyler Mahle settled down after the first inning to blank Colorado on five hits over the next six innings and worked out of a jam in the seventh. Garrett Hampson led off with a triple but Mahle stranded him at third.
“We’ve been getting the big hit lately. Tonight it didn’t come our way,” Rockies manager Bud Black said. “We had multiple opportunities to get a base hit, to do some situational hitting, just didn’t happen tonight.”
Mahle allowed two runs and seven hits and struck out four in his seven innings.
Reds: INF Mike Moustakas (heel contusion) did not play. ... OF Scott Heineman was added to the taxi squad for the last two games of the series.
Rockies: OF Charlie Blackmon wasn’t in the starting lineup due to a mild right groin strain suffered Friday night. He pinch-hit in the seventh and struck out. ... INF Brendan Rodgers (right hamstring) went 2 for 3 for Triple-A Albuquerque on Friday night in a rehab assignment.
SHOGO SAVES THE DAY
Hampson sent a drive to deep center with two outs in the bottom of ninth that looked destined for extra bases until Shogo Akiyama made a leaping catch to end the inning.
He got a bear hug from Jesse Winkler at the warning track and a tip of the cap from reliever Tejay Antone.
“I didn’t think he had a chance off the bat and he kept tracking it,” manager David Bell said. “He has that ability to close on the ball but then also it’s like he almost hangs a little bit in the air. It’s a beautiful play to watch. He was just gliding. There’s nothing like a great defensive play like that.”
LONG TIME, NO START
Chacín, normally in the role of long reliever, made a spot start for Colorado and allowed two runs on four hits in four innings. It was his first start for the Rockies since June 28, 2014, and in between he pitched for six teams over six seasons.
Chacín threw 53 pitches and got nine of his 12 outs on ground balls, including one double play. The other three were retired with strikeouts.
Fantasy baseball: Mariners on the move
Eric Karabell takes a look at Seattle's decision to deal away Kendall Graveman and why the team may not yet be done wheeling and dealing.
2021 MLB trade deadline tracker, rumors, news, analysis and latest buzz
July 30 is approaching fast. Here's the freshest intel we're hearing, reaction to completed deals and what to know for every team.
Fantasy baseball forecaster: Team hitting ratings
Stay ahead of the game and optimize your fantasy baseball hitters with our forecaster, which provides a rolling 10-day outlook of every team's hitting matchups as well as the potential for stolen bases.
Fantasy baseball forecaster: Pitcher projections for the next 10 days
Keep up to date on who is pitching -- and how well they're expected to do -- with our forecaster, which provides a rolling 10-day outlook of every team's probable starting pitchers with game score projections.
Fantasy baseball: Preparing for a middle-infield surge
Tristan H. Cockcroft takes a look at three potential names to target in order to improve the quality of your middle-infield options, all of whom may see increased action once the trade deadline passes.
MLB trade deadline - Where things stand for the four Chicago Cubs stars who could be dealt this week
Is this the last week of Bryzzo in Chicago? Which contender is most likely to land Craig Kimbrel? Here's what we know about the team that could be the talk of this deadline.