CINCINNATI — Head down, lips drawn tight, Dan Haren did his best to keep a straight face as he rounded the bases. The right-hander had just ended a month of good moments with another one that made him want to break into a big, beaming smile.

That would have to wait.

Haren connected on his first career homer Tuesday night, then tried to keep his emotions in check as he rounded the bases during a 6-2 victory over the Cincinnati Reds that ended the Arizona Diamondbacks’ longest losing streak of the season.

No surprise that Haren (7-5) had the most to do with it.

‘‘A great night for Dan Haren,’’ manager A.J. Hinch said. ‘‘He’s really remarkable in how he brings his best to the table every game. Even his second- and third-best nights are better than most. Tonight, he could throw the ball anywhere he wanted. He could throw any pitch. And he also did plenty of damage with his bat.’’

The right-hander was the NL’s stingiest pitcher in June and the one thing the Diamondbacks could count on. Heading into Tuesday’s game, they had dropped five in a row and eight of nine, done in by the major leagues’ worst defense and one of the NL’s worst offenses.

Haren gave up a run and four hits in seven innings, lowering his ERA to 2.19, the best in the league. He also hit a solo homer off Bronson Arroyo (8-7), who is having a rough time in June.

Miguel Montero hit a two-run homer off Arroyo in the sixth, a high, arching shot to center that landed an estimated 422 feet away. Up came Haren, who hit Arroyo’s next pitch — a hanging changeup — into the first row of seats in left field for a 6-0 lead.

‘‘When he hit it, I was like, ’Oh, he’s got a chance!’’’ Montero said. ‘‘We were all yelling at him when he got into the dugout.’’

Home runs involve bragging rights among Diamondback pitchers, who have a friendly competition that includes putting up a little money when one of them goes deep.

‘‘I was thinking about how much money the other starting pitchers owe me for that hit,’’ Haren said, declining to give any more details about their arrangement. ‘‘(Jon) Garland has one. (Jon) Rauch has one off Roger Clemens — that’s pretty cool. Rauch welcomed me to the home run club.’’

Montero also had a pair of singles, helping Arizona end its streak of five straight losses against Cincinnati. Mark Reynolds added three hits, including a two-run single.

Haren has been one of the few dependables for the injury-decimated Diamondbacks, mired in last place in the NL West. He had the Reds guessing wrong most of the time, retiring the first 11 in order — four of them on called third strikes that dusted the corners. Jay Bruce got Cincinnati’s first hit with two outs in the fifth, lining a single to center. It was only the second ball that Cincinnati got out of the infield.

Ramon Hernandez’s double in the seventh ended the shutout. Haren went 3-1 in six June starts, allowing only eight earned runs — the stingiest performance by any NL starter in the month.

For one night, it was more about one swing.

‘‘The home runs are going to be special,’’ Haren said. ‘‘I don’t know how many I’ll hit in my career. It was cool running around the bases.’’

Brandon Phillips had a sacrifice fly in the eighth, when the Reds loaded the bases but managed only one run.

For Arroyo, it was a month of much misery. The right-hander went 1-4 and was hit hard. He gave up three homers in an 8-2 loss in Toronto on Wednesday, lasting only 3 2-3 innings, and allowed six runs in 5 1-3 innings against the Diamondbacks.

‘‘I had good stuff today,’’ Arroyo said. ‘‘I felt pretty good. I’m just having a hard time getting into the groove.’’

It could have been worse: Arizona had two runners thrown out at the plate while Arroyo was in the game.

NOTES: Haren left for a pinch hitter after throwing 111 pitches. … Arizona activated 1B Chad Tracy from the disabled list. He missed 27 games with strained muscles in his right side. Hinch plans to start him on Wednesday. RHP Leo Rosales was optioned to Triple-A. … The Diamondbacks have four sets of back-to-back homers this season. … Reds manager Dusty Baker expects 3B Edwin Encarnacion to continue his rehab assignment in the minors for the rest of the week. Encarnacion went on the DL on April 28 with a chipped bone in his left wrist.

Reds’ boxscore

Tuesday’s Game

Diamondbacks 6, Reds 2

Arizona Cincinnati

ab r h bi ab r h bi

FLopez 2b 5 0 1 0 Taveras cf 4 0 1 0

S.Drew ss 5 1 0 0 HrstnJr 3b 4 0 1 0

J.Upton rf 5 1 2 0 Votto 1b 3 0 1 0

Rynlds 3b 5 1 3 2 BPhllps 2b 3 0 0 1

GParra lf 5 0 1 1 L.Nix lf 4 1 1 0

CYoung cf 2 0 0 0 RHrndz c 4 0 1 1

Clark 1b 3 1 0 0 Bruce rf 4 0 1 0

Monter c 4 1 3 2 Janish ss 2 0 0 0

Haren p 2 1 2 1 Fisher p 0 0 0 0

ARomr ph 1 0 0 0 Gomes ph 1 0 0 0

T.Pena p 0 0 0 0 Burton p 0 0 0 0

Schnws p 0 0 0 0 Roenck p 0 0 0 0

Rauch p 0 0 0 0 Dickrsn ph 1 0 0 0

Qualls p 0 0 0 0 Arroyo p 1 0 0 0

Richar 3b 1 1 0 0

Totals 37 6 12 6 Totals 32 2 6 2

Arizona 003 003 000 — 6

Cincinnati 000 000 110 — 2

E—B.Phillips (7), Burton (1). LOB—Arizona 10, Cincinnati 6. 2B—Reynolds (16), Haren (4), Hairston Jr. (10), L.Nix (18), R.Hernandez (11). HR—Montero (4), Haren (1). CS—G.Parra (3). S—Haren. SF—B.Phillips.

IP H R ER BB SO

Arizona

Haren W,7-5 7 4 1 1 1 9

T.Pena 1-3 1 1 1 1 0

Schoeneweis 0 1 0 0 0 0

Rauch H,2 2-3 0 0 0 0 0

Qualls 1 0 0 0 0 1

Cincinnati

Arroyo L,8-7 5 1-3 10 6 5 4 2

Fisher 1 2-3 1 0 0 1 3

Burton 1 1 0 0 0 1

Roenicke 1 0 0 0 0 1

Schoeneweis pitched to 1 batter in the 8th. Umpires—Home, Dana DeMuth; First, Hunter Wendelstedt; Second, Brian Knight; Third, Doug Eddings. T—3:01. A—22,725 (42,319).).