MIAMI (AP) _ Vladimir Guerrero hit a rocket, but it was just another dud for the Montreal Expos.

Both locker rooms were abuzz when asked about Guerrero's 452-foot bomb into the left-field upper deck of Pro Player Stadium, but the Expos lost 5-4 in 10 innings to the Florida Marlins on Tuesday night.

``I told him that's how I used to hit them with the wind blowing in,'' laughed Expos manager Felipe Alou. ``It wasn't a fly, but a rising line drive. It went 442, but if it didn't hit anything there's no telling how long it would've gone.''

Cliff Floyd singled in the winning run in the 10th to extend the Expos' losing streak to four games, but more significantly enabled the Marlins (74-82) to become the first NL team in 30 years _ and second in 50 _ to improve by at least 10 games in successive seasons, excluding strike-shortened seasons.

``It was the most important win of the season because the players know how important it was to me,'' said Marlins manager John Boles, whose club was 54-108 in 1998, the year after the World Series champs were dismantled, and 64-98 last season.

Luis Castillo walked against Steve Kline (1-5) leading off the 10th, took third on Mark Kotsay's bloop single to right center and scored on Floyd's soft single between first and second.

Antonio Alfonseca (5-6) pitched a perfect 10th for the win. The game drew just 8,538.

Florida's Ryan Dempster struck out seven in seven innings, raising his total to 206, one more than the previous team record set by Kevin Brown in 1997. Dempster allowed four runs and six hits.

``That's the hardest ball ever hit off me,'' Dempster said of Guerrero's long homer. ``He Guerrero hits mistakes and that was a mistake. He smoked it.''

Alex Gonzalez's three-run homer put Florida ahead in the second, but Guerrero hit a two-run homer in the fourth, extending his team record.

``I hit it sweet,'' was Guerrero's brief assessment.

``That ball might've put a hole in somebody,'' Montreal starting pitcher Dustin Hermanson said. ``When he gets the ball on the sweet spot, the ball's got a mind of its own.''

Orlando Cabrera's two-run single gave Montreal a 4-3 lead in the sixth, but Florida tied it in the bottom half when Floyd singled and scored on Mike Lowell's two-out double, running through third-base coach Fredi Gonzalez's stop sign.

Even Boles appreciated Guerrero's prodigious homer.

``When a ball is hit that long and far it usually has a flight attendant on it,'' Boles said.

Alou felt that if Guerrero played back in his days, he'd win the triple crown with his statistics.

``What a batter he is,'' Alou said. ``He's got triple crown statistics.''

Notes: When Dempster struck out Wilton Guerrero in the first, he became the second Canadian pitcher to reach 200 strikeouts in a season, joining Fergie Jenkins, who did it from 1967-71 and in 1974. ... The Marlins promoted Bill Singer from national crosschecker to scout. Singer pitched for 16 years in the major leagues. ... The Marlins are 32-20 in one-run games.