Pinch hitter Denny Walling hit a three-run homer and Ray Knight hit a game-winning, two-run single as the Houston Astros rallied for five runs in the ninth inning last night in Pittsburgh to take a 6-5 victory over the Pirates in the first game of a doubleheader. Joe Niekro and Bill Dawley then combined on a seven hitter to give Houston the sweep, 2-1.

John Candelaria cruised into the ninth of the first game with a six-hitter and a 5-1 lead, but Jerry Mumphrey and Alan Ashby singled and Walling chased the Pirates' starter with his second homer of the year. Cecilio Guante gave up a double to pinch hitter Terry Puhl before getting the first out of the inning. Kent Tekulve (6-4) then replaced Guante and gave up a single to Dickie Thon, who stole second. Rod Scurry took over and struck out Jose Cruz before Knight singled to left.

In the nightcap, Niekro (11-10) gave up a first-inning run, then worked out of jams in the third, fourth and fifth innings. Dawley came on after Niekro walked the leadoff batter in the seventh and went on to post his 12th save with three innings of one-hit relief.

It marked the first time in 21 years Houston had swept the Pirates in a doubleheader, the last coming on June 3, 1962. The loss was the fifth in six games for Pittsburgh.