Bartoli got the better of his three breakaway companions in the sprint to win this fifth leg of the series, a 254.4km stretch in the south of The Netherlands, in six hours 49 minutes and 17 seconds.
It was a photo-finish however with Bartoli adjudged as getting the better o second-placed team-mate Sergei Ivanov of Russia by just half a wheel. Michael Boogerd came third and American triple Tour de France winner Lance Armstrong crossed the line in fourth position.
"I was expecting this victory," Bartoli said afterwards. "I haven't had great luck till now and I have mucked up all my other races this season. The good form may have come a little late but I feel I have got what I deserved."
The main bunch sprint was won by reigning world road race champion Oscar Freire of Spain who earned fifth place, 52 seconds adrift of the leaders.
The 1999 winner Boogerd attacked at Eyserbos, 39 kilometers from the finish. Fellow Dutchmen Bram Schmitz and Bram De Groot had been the last riders to hold on in a six-man break after just 14 kilometers under driving morning rain, but were caught at Keutenberg, about 30 kilometers from the finish.
Over the closing stages, both Bartoli and Ivanov made attempts to go clear but impressive Armstrong was able to respond each time.
The 31-year-old Bartoli has been the world's No. 1 cyclist but, since a bad fall in the Tour of Germany three years ago, has not found it easy to get back his old form.
The Tuscan rider now has five World Cup races to his credit The Tour of Flanders in 1996, the Liege-Bastogne-Liege in 1997 and 1998, and the Zurich Championships in 1998. He has also twice been winner of the overall World Cup standings in 1997 and 1998.
Top 20 results, Amstel Gold Race cycling classic (159 miles):
1. Michele Bartoli, Italy, 6 hours, 49 minutes, 17 seconds.
2. Sergei Ivanov, Russia, same time.
3. Michael Boogerd, Netherlands, same time.
4. Lance Armstrong, United States, same time.
5. Oscar Freire, Spain, 6:50:09.
6. Peter Van Petegem, Belgium, same time.
7. Jo Planckaert, Belgium, same time.
8. Paolo Bettini, Italy, same time.
9. Erik Zabel, Germany, same time.
10. Nico Mattan, Belgium, same time.
11. Marcus Ljungquist, Sweden, same time.
12. Marc Lotz, Netherlands, same time.
13. Geert Verheyen, Belgium, same time.
14. Igor Astarloa, Spain, same time.
15. Eddy Mazzoleni, Italy, same time.
16. Cristian Moreni, Italy, same time.
17. Bram Schmitz, Netherlands, same time.
18. Daniele Nardello, Italy, same time.
19. Christophe Brandt, Belgium, same time.
20 Rolf Huser, Switzerland, same time.
World Cup Standings after five events:
1. Johan Museeuw, Belgium, 170 points.
2. Paolo Bettini, Italy, 134.
3. Peter van Petegem, Belgium, 121.
4. Mario Cipollini, Italy, 120.
5. Andrea Tafi, Italy, 109.
6. Michele Bartoli, Italy, 100.
7. George Hincapie, United States, 88.
8. Jo Planckaert, Belgium, 87.
9. Fred Rodriguez, United States, 79.
10. Oscar Freire, Portugal, 76.