"That's what is so frustrating," Reds manager Dusty Baker said.
Enjoying a solid outing to that point, Arroyo had Kaz Matsui down in a quick 0-2 count. But Matsui battled for an 11-pitch at-bat, including six foul balls, and connected for a single to center field.
Miguel Tejada followed by hitting an 0-2 breaking ball for a single to center field. Lance Berkman was hit by a 2-2 pitch to load the bases for Lee, who is second in the National League in RBIs.
"I felt like I was commanding the game really nice," Arroyo said. "The Matsui at-bat was big for them. He fought me all day. Tejada, I had him 0-2. I left a breaking ball over the plate, which was a huge mistake. I don't want to see Berkman or Carlos Lee with men on base. Both of those guys have definitely hurt me enough in the past."
Lee hit a 1-0 sinker and launched it hard off the facade behind the left field Crawford Box seats for the grand slam.
"I think with the bases loaded, not wanting to go 2-0 was in my mind a little bit, and I just left it a little too fat," Arroyo said.
A 1-1 tie was broken wide open, and the Reds (50-58) went on to lose their fifth straight game. The defeat moved them back into the National League Central cellar after the Pirates won their game with the Rockies.
"That wasn't a bad pitch. That was just good hitting by El Caballo," Baker said. "There were a couple of bad pitches that preceded that."
Arroyo gave up six earned runs and eight hits over 6 1/3 innings without a walk and three strikeouts. The other homer he allowed was on a 2-0 breaking ball to Tejada with two outs in the third inning.
After finding out the Reds had dropped the previous seven games to the Astros (50-56) dating back to last season, Baker tried altering his lineup. Besides the sitting of Edwin Encarnacion, Ken Griffey Jr. and his 11-game hitting streak were rested.
It was to no avail against Astros starter Brian Moehler, who pitched 8 2/3 innings for the victory. Coming into the night, Moehler had unimpressive career numbers vs. Cincinnati, going 0-4 with 6.82 ERA in eight games, including five starts.
Moehler (6-4) gave up two runs and seven hits but rarely seemed in trouble. In the top of the third, Joey Votto hit a leadoff double and scored on Arroyo's two-out double down the left-field line. In the top of the ninth, Brandon Phillips' groundout scored Jeff Keppinger.
"He threw a good ballgame," Baker said. "A lot of people are throwing good games against us lately."
The Reds went 1-for-8 with runners in scoring position. In the seventh, after he hit a one-out double, Jolbert Cabrera was nailed in a double play after running on contact on Votto's lineout to shortstop.
"I asked [Cabrera] if he thought there were two outs," Baker said. "He said, 'No' and he thought the ball was going over his head. If it goes over his head, he's going to score anyway. He was probably overplaying some in that situation."
All of this happened in front of Reds owner Bob Castellini, who made an unexpected personal visit to Houston to try to buck up his sagging club, which has fallen to a season-high-tying 13 1/2 games out of first place.
Arroyo has been rumored as trade bait for contending clubs needing a starter and voiced his desire to remain in Cincinnati last week. Before the game, Castellini indicated there was no interest in moving Arroyo, despite rumors to the contrary.
"I'd rather Bronson Arroyo be here next year than me," Castellini said. "He's been one of our shining stars here lately."
Indeed. Arroyo came into the start 5-0 with a 3.09 ERA over his previous five starts. Overall, he is 9-8 with a 5.74 ERA.
Arroyo talked with Castellini personally about his situation before the game.
"He told me. I'm happy," Arroyo said. "I wouldn't have said what I said in the papers the other day if I didn't mean it. I've enjoyed my time here. Even though my three years have been three losing seasons thus far, I really think we can do something in this division in the near future. I'd like to be a part of it."