Chavez (3-1, 2.44 ERA) has been superb in his eight starts, striking out 51 and walking 12 in 51 2-3 innings.
"It's what he's been doing all year for us," Melvin told MLB's official website. " ... He throws the ball where he wants to. He's focused and taking advantage of this opportunity."
The right-hander allowed two runs in a career-high eight-plus innings of a 5-4 win over the Chicago White Sox on Monday, earning praise from White Sox manager Robin Ventura.
"He throws a lot of strikes," Ventura said. "Either you're going to have to swing at them or it's probably going to be strike three really quick."
Chavez has compiled an 8.49 ERA in 10 relief appearances against the Indians (19-24) going into his first career start in the series. However, he may have a favorable matchup in a Cleveland team that's been outscored 21-5 during a three-game losing streak.
''That's just the luck of the draw we're having right now,'' Indians reliever Marc Rzepczynski said. ''But starting a homestand with two losses to Oakland, you definitely didn't want that to happen.''
The A's (27-16) will be looking for Chavez to go deep into Sunday's contest after Scott Kazmir was ejected in the second inning of a 6-2 victory Saturday. Dan Otero, Fernando Abad, Luke Gregerson and Sean Doolittle stepped up to throw 7 2-3 innings of one-run ball.
"I think that kind of inspired us a little bit," said Donaldson, whose team has won eight of nine by a combined 58-15 score. "I don't take that lightly when you throw our starting pitcher out in the second inning."
The A's will try to stay hot against Masterson (2-2, 4.31), who had won back-to-back home starts before yielding five runs over 5 1-3 innings of Tuesday's 5-4 loss at Toronto.
While Masterson owns a 5.55 ERA on the road, he's posted a 2.05 mark over his last four home outings.
The right-hander has gone 2-6 with a 6.97 ERA in nine career starts against the A's, but threw seven innings of three-hit ball in a 2-0 win at Oakland on opening day March 31.
Masterson has baffled several of Oakland's hitters, including Josh Reddick (4 for 21), Alberto Callaspo (4 for 23), Jed Lowrie (2 for 14) and Donaldson (1 for 12). Coco Crisp and John Jaso are a combined 9 for 27 with four homers against him, though.
The Indians could get a much-needed offensive boost from veteran designated hitter Jason Giambi (strained right calf), who will likely be activated from the 15-day disabled list Tuesday.
''I know we're kind of sputtering,'' Giambi said. ''We get that little glimmer and then it kind of falls apart. We have to keep our heads above water until we hit that good winning streak.''