HOUSTON -- Roy Oswalt came off the disabled list and beat Cincinnati again, striking out five in the Houston Astros' 5-4 win over the Reds on Monday night.

Associated Press

Roy Oswalt earned his 20th career victory against the Reds.

Oswalt (8-8) won his fifth straight start against the Reds and improved to 20-1 in 25 career outings against them, despite giving up a grand slam to Adam Dunn. The Houston ace threw 74 pitches in five innings in his first start since aggravating a left hip injury on July 11.

He went on the DL on July 19 and was activated just before Monday's game.

Geoff Blum hit his third homer in two days and Jose Valverde pitched a perfect ninth to earn his 27th save. The Astros' bullpen allowed one hit in four scoreless innings as Houston beat Cincinnati for the seventh straight time.

Johnny Cueto (7-10) gave up five runs and eight hits for the Reds, who've lost four in a row and six of their last eight.

The Astros took a 2-0 lead before Cueto recorded his first out. Kaz Matsui led off with a double and scored on Miguel Tejada's single up the middle. After Lance Berkman walked, Carlos Lee blooped an RBI single to center.

Blum lined out to center and Berkman tagged up from third to make it 3-0. Cueto threw 33 pitches in the first inning.

Jay Bruce beat out an infield single to start the Reds' rally in the third. Ken Griffey Jr. singled and Brandon Phillips walked to load the bases for Dunn, who came in hitting .324 since the All-Star break.

Dunn hammered the first pitch off the center-field wall, above the yellow line for a home run. The 426-foot shot was Dunn's ninth career grand slam and his second in less than a week. He also hit one on July 23 against San Diego.

It was the second grand slam allowed by Oswalt in his career and the first since Cliff Floyd hit one for the New York Mets at Minute Maid Park on May 14, 2004.

Berkman doubled in the Houston third before Blum homered to right center, his ninth of the season and third in two games. Blum hit a pair in the Astros' 11-6 win over Milwaukee at Miller Park on Sunday.

Tim Byrdak, Geoff Geary and Wesley Wright combined to pitch three innings of one-hit relief, paving the way for Valverde. Berkman made a diving catch on Javier Valentin's liner for the final out.

Notes:@ Griffey has an 11-game hitting streak. ... The Astros have won 12 of the last 15 meetings with the Reds. ... The Astros activated Oswalt from the disabled list before the game and optioned RHP Runelvys Hernandez to Triple-A Round Rock. Hernandez started four games and went 0-3 with an 8.38 ERA in 19 1-3 innings. ... Astros CF Michael Bourn sat out with a sprained right ankle. Cooper said Bourn could return to the lineup on Tuesday, but "that's not a for-sure thing."