MIAMI -- Marlins manager Don Mattingly had seen rookie right-hander Luis Castillo on tape and had read the reports.

Then, on Sunday afternoon, the Miami Marlins had to face the pitcher who had been in their organization until he was traded, along with two other prospects, to the Cincinnati Reds in January.

Castillo beat his former organization and catcher Tucker Barnhart produced a season-high three RBIs as Cincinnati snapped a six-game losing streak with a 6-4 win over Miami on Sunday at Marlins Park.

Castillo (2-4) lasted a career-high eight innings. He allowed three hits, one walk and one run, striking out six. He is one of 13 rookie pitchers -- including eight starters - the Reds have used this year.

"Pretty favorably," Mattingly said when asked how Castillo looked in comparison to the scouting reports, "a guy throwing 100 (mph) who doesn't walk many batters.

"He used everything. He got his breaking ball over. He got his changeup on lefties. His velocity is something you've got to get going for."

Dan Straily (7-7), the player Miami received in the Castillo deal, lost his third straight start. He allowed seven hits, two walks and two runs in six innings.

"I was pretty excited that we were lined up to pitch against each other," Straily said of Castillo. "It's always fun when you get to match up against guys you've been traded for -- I've faced (St. Louis Cardinals outfielder) Dexter Fowler a few times. It's just another layer to baseball."

Castillo noted how he and Straily both wear No. 58 and added that he knows almost all of the Marlins players very well.

"It's amazing," Castillo said. "You face your ex-team. You face the pitcher you were traded for, and we wear the same number on the back of our jerseys. Thank God everything worked out for me today."

The Marlins (49-54) had their four-game win streak snapped. They had won eight straight games against the Reds at Marlins Park, setting a franchise record against any opponent.

This would've been just the 11th four-game sweep in Marlins history and the first against the Reds.

Instead, the Reds (42-63) improved to 3-14 since the All-Star break.

Cincinnati opened the scoring with a two-run second inning. Eugenio Suarez drew a leadoff walk, advanced to second on a single by Jose Peraza and scored when Barnhart golfed a 1-2 pitch to right for an RBI single.

Peraza scored when Castillo bunted on a safety squeeze. It was Castillo's first career RBI.

Straily suffered an undisclosed injury while fielding the bunt but remained in the game and escaped further trouble with a strikeout and a ground out, both with the bases loaded.

"My hamstring just grabbed real quick, a cramp," Straily said. "I wasn't going to throw another pitch until that was gone because then you would be leaving yourself vulnerable for another one."

Miami cut its deficit to 2-1 when Dee Gordon drew a walk and scored when backup catcher A.J. Ellis drilled a double over the glove of diving center fielder Billy Hamilton.

The threat ended when Christian Yelich's swing produced a two-foot grounder. Barnhart pounced on the ball, tagged Yelich -- who hadn't moved out of the box -- and threw out Ellis at third base for a double play.

Cincinnati extended its lead to 6-1 with a four-run seventh. Reliever Hunter Cervenka loaded the bases with no outs by allowing a single and two walks. Rookie reliever Drew Steckenrider inherited the mess, and the Reds capitalized with an RBI groundout by Adam Duvall, Peraza's RBI walk and Barnhart's two-run single.

The Reds held on despite Marcell Ozuna's three-run homer with one out in the bottom of the ninth off of reliever Raisel Iglesisas. Ozuna has 24 homers -- a career high -- and 81 RBIs this season. His 27 RBIs this month are a franchise record for July.

"It was good to put together a win," said Barnhart, Cincinnati's hitting hero. "I've been scuffling. I haven't felt like myself. This was a step in the right direction."

NOTES: Marlins C J.T. Realmuto hit his 12th homer of the season Saturday, breaking his previous career high of 11 set last year. Realmuto is fourth in the NL and eighth in the majors in homers by a catcher this year. ... RHP Merandy Gonzalez, 21, is considered the top prospect Miami received when they traded closer A.J. Ramos to the New York Mets. Gonzalez is 12-3 with a 1.78 ERA in 17 Class A starts this year. Miami also got CF Ricardo Cespedes, 19, who was hitting .255 in rookie league. The Marlins on Monday start a three-game series against the NL East-leading Washington Nationals. The teams have split six games this year. ... The Reds start a three-game series at the Pittsburgh Pirates on Tuesday. The Reds lead the season series 6-1. ... Reds RHP Homer Bailey, who starts Tuesday, has lost three straight starts, allowing 17 runs (15 earned) in 16 innings.