Chicago starter Scott Sanderson was locked in a 0-0 duel with New York's Ron Darling through five innings yesterday at Shea Stadium. Hardly had Sanderson withdrawn with a flareup of his chronic back spasms than the Mets came up with a five-run sixth, climaxed by Hubie Brooks' home run with two on base, to defeat the Cubs, 5-1.

The Cubs' lead over the second-place Mets in the East Division now is six games with 19 games remaining for each team.

Darling (12-6) allowed six hits and struck out eight before being replaced by Jesse Orosco after giving up a leadoff homer to Gary Matthews in the top of the ninth.

Sanderson had checked the Mets on four hits, but Mookie Wilson opened the sixth with a triple off George Frazier (5-3) and scored when Keith Hernandez doubled to right-center. Darryl Strawberry reached on a third-strike wild pitch. George Foster hit a run-scoring single and Brooks greeted Warren Brusstar with his 15th homer.

"If we had lost today the only way the Cubs could blow this thing would be to fold up their tent, the way the 1964 Philadelphia Phillies did," said Hernandez.

The Cubs got four doubles off Darling, but twice failed to move the runner to third and once saw a runner thrown out trying to stretch the hit. That was Keith Moreland in the second inning, cut down at third on a strong relay from left fielder Foster to shortstop Brooks to third baseman Ray Knight.

Brooks handled several tough chances afield.

"I know I was being second-guessed when I moved Hubie from third base after the (Aug. 29) deal for Ray Knight," Mets Manager Dave Johnson said. "To me, it was the most logical move in baseball . . . Hubie's an outstanding athlete with good hands. He's also quicker than people think."

The Mets activated shortstop Rafael Santana from the disabled list today and plan to do the same with Ron Gardenhire, another shortstop, Monday. Does that send Brooks back to third?

"He stays at short," Johnson answered. "I haven't seen anything that would make me change my mind. I'm also happy with Knight at third. To me Hubie's more comfortable now than when he was playing third."