Jerry Morales singled in the go-ahead run and Ryne Sandberg followed with a two-run triple yesterday, highlighting a four-run eighth inning that led the Cubs to an 8-5 victory over the Philadelphia Phillies for a sweep of their three-game series in Chicago.

The victory was Chicago's fourth straight, equaling the Cubs' longest winning streak of the season. It was also the fourth straight loss for the Phillies.

With the Phillies ahead, 5-4, Jay Johnstone opened the eighth for the Cubs with his second homer of the game, off losing reliever Tug McGraw (1-2). Jody Davis followed with a single and moved to second on a sacrifice. Pinch-hitter Keith Moreland was intentionally walked and McGraw got Junior Kennedy to fly to center for the second out.

Morales, batting for Scot Thompson, singled to right, scoring Davis with the go-ahead run. Sandberg followed with a triple to center, bringing home Moreland and Morales.

Dick Tidrow (5-2) worked 1 1/3 innings for the victory and Lee Smith pitched the ninth, gaining his sixth save.

Philadelphia scored four runs in the third on a two-run single by Gary Matthews and RBI base hits by Mike Schmidt and George Vukovich.

The Cubs tied at 4 in the sixth on Johnstone's three-run homer off starter Mike Krukow and an RBI triple by Steve Henderson.

Philadelphia moved ahead, 5-4, in the seventh on a run-scoring single by Bo Diaz, which scored Pete Rose from second.