Keith Hernandez tripled home two runs in a four-run first inning and the New York Mets pushed across the tie-breaking runs in the fifth with the help of an error as they beat the Montreal Expos, 9-4, last night in New York.

That done, they awaited the outcome of the St. Louis Cardinals-Chicago Cubs game. The Cardinals won, 4-2.

"We're gonna need help," said the Mets' manager, Davey Johnson, who watched the end of the Cardinals game on TV in his office. "Our chances are slim, especially the way the Cards are playing. I still have hope. Funnier things have happened in pennant races."

The Mets remain two games behind first-place Cardinals in the NL East. Each team has two games left. If they end the regular season tied, they would play it off Monday at Shea Stadium.

The Mets will start Ron Darling (16-5) today against the Expos' Floyd Youmans (3-3).

"It would take a miracle for us to win it now," Hernandez admitted. "I'm hitting as well as I can hit. The adrenaline is there. When you're playing for a pennant, you just don't let up."

Hernandez, who had five hits in Thursday night's loss in St. Louis, tripled home two runs to give the Mets a lead in the first inning of last night's game. The runs came off right-hander Bill Gullickson (14-12).

One out later, Darryl Strawberry, who had three RBI in the game, looped an RBI single to left. George Foster followed with another RBI base hit to give left-hander Sid Fernandez a quick 4-0 lead.

Fernandez couldn't hold it, though, and Tim Raines' two home runs helped tie the game at 4.

"He just didn't have it tonight," Johnson said of Fernandez, who still managed to get the victory.

The Mets went ahead to stay in the bottom of the fifth after second baseman Vance Law booted Mookie Wilson's double play grounder to put men on first and second with nobody out.

After Wally Backman sacrificed, Hernandez was walked intentionally to load the bases. Gary Carter drove in the go-ahead run with a squib single over the pitcher's mound for his 100th RBI this season, then Strawberry's sacrifice fly put the Mets up by 6-4. In other games, Johnny Ray hit a three-run homer to lead the Pirates over the Phillies, 7-2, in the first game of a doubleheader in Philadelphia, then Tom Foley won the second for the Phillies, 8-5, with a three-run homer; in Los Angeles, Wayne Krenchicki's grand slam won for the Reds, 4-2; Roger Mason's four-hitter for the Giants beat the Braves, 1-0, in San Francisco; and in San Diego, Mario Ramirez homered to enable the Padres to beat the Houston Astros, 4-3.