The Indians have won seven of nine, while Oakland has dropped 20 of 24 -- including a pair of eight-game skids. The Athletics (17-32) tied the 1979 team for the second-worst mark after 49 games since the club moved to Oakland in 1968. The 1994 Athletics started 13-36.
Westbrook (2-7) won for the first time in five starts. He allowed four hits and one run, walked three and struck out three.
"My stuff was OK, nothing special," Westbrook said. "I have pitched a lot better than this and lost. Of all the games I've pitched well this year, this was probably the worst."
The right-hander, a 2004 AL All-Star when he went 14-9 with the third-lowest ERA in the league at 3.38, has received little offensive support this year. He has allowed two or fewer earned runs in eight of his 11 starts, but the Indians averaged only 2.2 runs in his first 10 outings.
"I can't dwell on that," he said. "A lot of that is out of my control. I just try and concentrate on my next start and go from there."
Matt Miller entered with two men on in the eighth and got pinch-hitter Bobby Kielty to ground out the end the inning. He allowed one run on two hits and a wild pitch in the ninth, but finished for his second career save and first since July 19.
Martinez, mired in a 4-for-37 (.108) slump coming in, doubled to open Cleveland's three-run fourth inning and hit his first homer in 119 at-bats in the sixth.
"This definitely was a good day for me, but I have to keep it going," Martinez said. "I'm still hitting in the low 200s (.201). I know that I can hit and I will hit."
The switch-hitter, also an All-Star last year when he hit .283 with 23 homers and 108 RBI, entered batting .147 (16-for-109) against right-handers, but went 2-for-3 against Seth Etherton (1-1).
"If I knew exactly what it was, I would not be doing it," Martinez said. "Sometimes, it just takes a while to feel comfortable at bat."
Oakland manager Ken Macha struggled to describe his team's slump, too. The Athletics are last in the AL in runs (186), homers (27) and batting average (.241).
"We have our work cut out for us," he said. "We tried to put a little rally together. In the majors, it is tough to string together 10 singles."
"That pitch was garbage," Etherton said of his 0-2 offering to Cora. "I tried to throw it outside and it was right over the plate."
Eric Byrnes hit a bases-loaded sacrifice fly in the Oakland sixth to cut the deficit to 4-1.
Westbrook beat Oakland for the first time in his career. He had been 0-5 with a 5.82 ERA in seven games, including six starts, against the Athletics.
Etherton allowed five runs and five hits over 5 1/3 innings. He walked four and struck out five.
The right-hander is the only Athletics starting pitcher to get a win in Oakland's last 24 games -- in a 13-6 victory over Boston on May 18.
- Oakland has not lost nine in a row since July 21-29, 1998.
- Oakland 1B Dan Johnson singled in the sixth inning for his first career hit in his third big-league game.
- Etherton is 0-2 with an 11.08 ERA in three career starts against Cleveland.
- Indians 3B Aaron Boone, hitting .159 for the season and in a 3-for-26 (.115) slide, did not play.
- Gerut has hit safely in nine of 11 games (13-for-35, .371) since returning from Triple-A Buffalo on May 18.