"I know it kind of stinks but I did see some of his strikeouts," Cust said.
Matt Holliday added a three-run shot and Bobby Crosby had three hits to help Oakland snap a four-game losing streak. Jack Hannahan doubled home a run and Kurt Suzuki added three hits in the A's highest-scoring game this season.
"He's got to do that to get ready for what he did," Cahill said. "It's what I do before a game."
The grand slam helped Cahill (1-2) enjoy his outing even more.
"I was a little more aggressive after that," said Cahill, who had his brother and girlfriend among the 13,702 in attendance. "A lead like that is nice and lets you relax."
Cahill, who entered the game tied for the AL lead for walks, did not issue a free pass while striking out four.
"No walks is definitely a huge step for me," Cahill said. "It's been my weakness my whole career. I felt like I was getting into a groove during my last start."
Cust just wanted to take advantage of the warm afternoon.
"It's nice when the weather heats up and the ball does travel better during the day," Cust said. "I've always liked hitting here in the day anyway."
Brandon McCarthy (3-1) allowed seven runs on seven hits and three walks.
"For three innings I thought he threw the ball well," Rangers' manager Ron Washington said. "He got out there in the fourth and the two walks hurt him. He left one up to Cust and he caught it. They beat us today. They swung the bats well."
Kris Benson pitched three innings in his first career relief appearance after 197 starts. Holliday greeted him with his fourth home run to give the A's an 8-1 lead. Benson gave up two runs on five hits.
After Cahill gave up Davis' solo shot in the fifth, he retired eight of his last nine batters. He never faced more than four batters in an inning and was the first Oakland starter to pitch into the seventh inning in 14 games.
McCarthy breezed through the first three innings and then ran into trouble in the fourth. Suzuki singled and Jason Giambi and Holliday each walked ahead of Cust's drive halfway up the right-field bleachers for his second career grand slam. Hannahan added a run-scoring double.
"Suzuki led off that inning with the hit and I kind of lost my mechanics a little bit," McCarthy said. "I threw some really non-quality pitches."
McCarthy's day was finished after Suzuki and Giambi singled to start the fifth. After Holliday made it a seven-run game, Crosby doubled home a run.
The Rangers scored three runs in the ninth, all charged to A's closer Brad Ziegler, taking advantage of Orlando Cabrera's fielding error and getting RBI doubles from David Murphy and Omar Vizquel and a run-scoring single from Jarrod Saltalamacchia, who had two hits.
- Holliday has four home runs in his past eight games after going homerless in his first 17.
- Cahill received three or fewer runs in his first five starts.
- Cust hit his other grand slam at Detroit on Aug. 10, 2007.
- McCarthy had a career ERA of 11.57 (five games) in Oakland.
- The Rangers have homered in all 14 of their road games.
- Young has hit safely in 18 of his last 19 games against the A's.