Yasmany Tomas hit two for the Diamondbacks who snapped the Reds' three-game winning streak and won for the first time in five games.
Jay Bruce hit his 21st home run in the ninth with two on against Tyler Clippard with no outs in the ninth to make the game close. Bruce had four RBI on the day to raise his season total to 73 to tie him with Nolan Arenado for the National League lead.
"We played a great series. We really did," Bruce said. "Today was a little bit of back and forth. No one could really solidify the game. We were in it right up until the end. We had a chance and that's really all you can ask for."
Clippard struck out Ramon Cabrera with the tying run on base to close out the game.
"It's been good this homestand," Bryan Price said. "There was that big rally against their closer. Cozart getting on base with the walk and on we go. Joey given us the great at bat and Jay hitting the home run. It was a situation where we were a homer away from walking them off. That says a lot. It was a hot day. We were down early."
The trading deadline is a week from today when the Reds conclude a road trip to San Francisco and San Diego. There is some question whether Bruce will return with the team of be traded.
"I made it clear from the beginning. My goal was to finish my career with the Reds. That hasn't changed," Bruce added.
Brandon Finnegan won his last two starts. He had hopes that the Arizona Diamondbacks would be his third straight victim in his first ever appearance against them.
"My last two outings I commanded the ball pretty well. It is just a rough patch. I just have to keep pushing. I've had a lot more better games than I've had bad games. I have to keep that in the back of my mind and have the confidence to go back out there my next start," Finnegan said.
The Diamondbacks started fast against the left-hander. Jean Segura walked to open the game. Phil Gosselin singled Segura to second. Reds' catcher Cabrera threw Segura out stealing third on a call that survived the review process. Rickie Weeks two-out single scored Gosselin.
The Reds went to work on Arizona starter Zack Godley. Billy Hamilton singled to open the game as a base runner for the third straight game, extending his hitting streak to seven games. Two ground balls sent Hamilton to third. Jay Bruce walked Adam Duvall drove in his 65th run with a single. Bruce scored when Brandon Phillips extended his hitting streak to 12 games with a single that gave the Reds a 2-1 lead.
Tomas tied the game with a line drive into the leftfield seats for his 14th home run.
Wellington Castillo hit a three-run home run in the third, his 11th to put the Diamondbacks up by three.
The Reds got to Godley for three runs in the bottom of the inning.
Jose Peraza was hit with a pitch. Joey Votto singled to hit in all nine games since the All-Star break. Bruce earned his 70th RBI with a ground single up the middle. Duvall's line drive to a leaping Segura at shortstop turned into a double play as Votto failed to get back to second. Phillips second single scored Bruce. Ivan De Jesus Jr. and Cabrera singled to allow Phillips to score the tying run.
Paul Goldschmidt's first hit of the series was his 17th home run leading off the fifth off Finnegan.
Tomas added his 15th against Josh Smith in the eighth inning.
Finnegan completed five innings for the third straight game but this time he left behind and could only get the lose.. He pitched five innings, allowing six earned runs on seven hits and two walks. Finnegan struck out three and allowed three home runs.
"There were a lot of misses. He tried to go in to righties," Price said.. "The ball was running back over the plate. It wasn't his best command day."
Finnegan allowed three of the four home runs.
"It was steamy. It felt like summer," Finnegan said.. "The heat didn't affect my control at all. My control was pretty good today actually. The three home runs were down right where Cabrera called them. I came in and looked at all three of the home run. The pitch that Goldschmidt hit was in on his hands it wasn't even on the plate. It just wasn't my day. Those three pitches were my best pitches of the day and they still got hit out. It's the product of playing in a small park."
Ross Ohlendorf relieved Finnegan. Brandon Drury and Tomas singled to greet him. Godley's sacrifice advanced the runners. Segura struck out swinging but the ball got away from Cabrera and Drury scored and Segura reached first. Cabrera threw Segura out at second on a steal attempt for the second time. Gosselin's double scored Tomas.
Godley pitched 5 2/3 innings and left with runners on first and third with two outs. Cabrera walked and Hamliton's second single put runners at the corner. Arizona manager Chip Hale brought in left-hander Zac Curtis to face left-handed hitters Votto and Bruce. Curtis walked Votto to load the bases but struck out Bruce to preserve the lead.
Godley allowed five earned runs on 10 hits and left with a lead that would make him 3-1 on the year.