CINCINNATI -- Facing one of the Majors’ hottest teams and a division rival while trying to halt a losing streak, the Reds reached deep and fought extra hard against the Cardinals on Monday night.

It showed as rookie Matt McLain dueled pitcher Jordan Montgomery in a 13-pitch at-bat in the fourth inning, despite ending it with a strikeout. It was obvious in the eighth inning, when manager David Bell went to closer Alexis Díaz while the game was tied at 5, seeking five outs.

It culminated in the bottom of the 10th inning, when the Reds finally landed a put-away punch. Nick Senzel's sacrifice fly to right field scored Spencer Steer and gave Cincinnati a 6-5 walk-off win over St. Louis to end a four-game losing streak.

"We needed that win. Back and forth game. We grinded it out," Senzel said.

The Reds, who dropped six of their past seven games, had leads of 2-0, 4-3 and 5-4 on Monday night and couldn't hold them.

"I think at the end of the year, every game matters," said Steer, who belted a two-run homer in the third inning. "You don't want to look back and be like, 'This is the one that is the difference maker.'"

The Cardinals evened the game in the top of the eighth inning when lefty reliever Alex Young gave up back-to-back one-out doubles -- including the game-tying RBI hit by Paul DeJong that made it a 5-5 game.

Bell summoned Díaz from the bullpen.

"I wanted to give us a couple of shots at [a win]," Bell said. "I was planning to bring him in anyway in the ninth at the top of the order, but why wait? Let’s see if he can get us out of that one."

Díaz finished the inning with a strikeout and a flyout while needing only six pitches. He opened the top of the ninth by walking Tommy Edman on four pitches and striking out Paul Goldschmidt on a slider. After issuing a free pass to Willson Contreras, Díaz recovered to strike out Nolan Arenado with another slider.

The third walk of the rally -- to Lars Nootbaar -- loaded the bases.

“I really didn’t have my fastball today," Díaz said through translator Jorge Merlos. "I couldn’t locate it as well as I would like to, so I just went with the slider and tried to focus on that and get that for outs right there."

Finally, Díaz made his big escape on his 34th pitch of the night by striking out Nolan Gorman to end the threat.

"Never a doubt with him," reliever Ian Gibaut said. "He's got that dog in him when he's out there fighting, fighting every pitch. … You trust that guy. He's the guy you win or die by in that situation. He showed that he's the best."

Gibaut, who gave up homers to the Yankees' Anthony Rizzo in losses on both Friday and Saturday, issued a walk and struck out two in the top of the 10th inning to earn the win.

“He did a phenomenal job right there to come in and just attack the hitters," Díaz said.

Opening the bottom of the 10th as the runner on second base, Steer received instructions from first base coach Collin Cowgill to watch for a ball in the dirt by Cardinals closer Ryan Helsley so he could advance. Helsley, in his second inning of work, did just that on his ball-four fastball to Tyler Stephenson, which got away just long enough for Steer to take third base with a head-first slide.

"[Helsley’s] one of the best closers in the game. He's a tough at-bat, so getting that extra 90 feet off of a guy like that is pretty crucial," Steer said. "I was just kind of looking for it, [trying to] be aggressive and just trust my instincts."

"What a read by Spence on ball four there. Heads up play," Senzel said. "We don’t finish that game off if it’s not for him."

On a 1-1 slider from Helsley that was up and away, Senzel lifted a sacrifice fly to right field that scored Steer for the winning run.

"It couldn’t have been a better approach at the plate than Nick had," Bell said.

The Cardinals, who spent time at the bottom of the National League Central division standings with a 10-24 start, entered Monday as winners in 11 of their previous 14 games.

"From the first pitch all the way to the end of the game, it felt like we all just put all of our 100 percent work into getting this victory -- all the guys, all the hitters, all the pitchers really did a great job getting that victory," Díaz said.