Butch Hobson slammed a three-run homer for his second hit of a nine-run seventh inning today as Boston battered Cleveland, 11-4, in the opener of a day-night double header.

In New York, the Yankees kept pace in the tight American League East race as Catfish Hunter pitched his first shutout of the season and beat Milwaukee, 7-0, in the first game of a doubleheader. Graigh Nettles' 21st home run, with two on base, staked Hunter to an early lead.

The homer was the 19th of the year for Hobson, who contributed three of Boston's 15 hits.

Trailing, 3-2, in the 100-degree heat, the Red Sox opened their seventh with George Scott's single. Scott eventually scored the tying run on a sacrifice fly. Rick Miller, who went 4-for-4, stroked a single to score Hobson, who had doubled for his first hit of the inning, to give Boston the lead. Fred Lynn doubled to chase Wayne Garland.

Rick Waits walked Jim Rice and designated hitter Carl Yastrzemski to load the bases. Then Carlton Fisk walked to force in a run. After Scott singled in two runs. Hobson greeted reliever Tom Buskey with his home run.

Luis Tiant, 6-7, went seven innings for Boston. He fanned eight, including Rico Carty in the fourth for the veteran hurler's 2000th career strikeout.

Andre Thorton tripled and scored on a sacrifice fly to give Cleveland a 1-0 lead, but Boston evened the score with three straight hits in the third.

The Red Sox got another run in the fourth when Hobson singled to score Yastrzemski. Cleveland regained the lead in the seventh on Larvel Blanks' two-run homer. Duane Kuiper's double scored Cleveland's final run in the ninth.

Nettles' blast in New York followed leadoff singles by Chris Chambliss and Reggie Jackson in the second inning off Brewer starter Jim Slaton. Nettles was robbed of another three-run homer off Slaton in the third when center fielder Von Joshua reached over the wall to grab his long drive.

Hunter (6-4) pitched a five-hitter. He struck out three, walked two and didn't permit a runner past second base.

The Yankees added two runs with two out in the fifth on Chambliss' triple and Jackson's single and two in the eighth, highlighted by Carlos May's run-scoring pinch-hit double.