Petrova, seeded 14th, had a surprisingly easy time with the Belgian star as she posted a 6-3, 6-2 victory in a match that lasted one hour and 24 minutes.
Petrova had 16 winners and closed out the match with her second ace before jubilantly throwing her hands up in the air.
"I'm very satisfied with myself," she said. "I played my game."
Nadia Petrova celebrates her upset win over Justine Henin-Hardenne.(AP Photo/Michael Kim)
Petrova broke Henin-Hardenne's serve on five times, including three in the first set.
Henin-Hardenne, the reigning Australian Open and Olympic champion, had just 14 winners and committed an unusually high 30 unforced errors in the lopsided match.
Henin-Hardenne became the first women's top seed to lose before the quarter-finals since Billie Jean King lost in the third round in 1973.
Petrova will be appearing in only her second quarter-final match in a Grand Slam when she battles fellow Russian Svetlana Kuznetsova.
Prior to Petrova's upset, fifth-seeded Lindsay Davenport doused 11th-ranked Venus Williams in 7-5, 6-4, needing five match points to do so.
The final game of the match turned out to be the best one of the day as Williams squandered five break-point opportunities and the two went to deuce on nine occasions.
Davenport finally advanced on her fifth match point as Williams sailed a forehand return just beyond the baseline.
Williams committed 22 more unforced errors (42-20) than Davenport'.
Up next for the sizzling Davenport will be unseeded Japanese Shinobu Asagoe.
The ninth-seeded Kuznetsova moved into the round of eight by handling 27th- seeded Frenchwoman Mary Pierce 7-6 (7-5), 6-2.
In other fourth-round action, the aforementioned Asagoe took out 29th-seeded Greek Eleni Daniilidou 7-6 (7-4), 4-6, 6-3 to reach her first-ever Grand Slam quarter-final.
MEN'S DRAW
Top-seeded Roger Federer reached the round of eight Monday without even lifting his racquet, while two-time champion Andre Agassi routed Sargis Sargsian to set-up a marquee quarter-final showdown.
Federer, from Switzerland, was scheduled to meet 16th-seeded Romanian Andrei Pavel on Monday, but the latter withdrew because of a herniated disc in his back.
Pavel missed six months of action last year with injuries to his back and right wrist.
Federer, who boasts an ATP-best eight titles this year, had never before advanced past the fourth round at Flushing Meadows, including fourth-round losses here in each of the last three years.
He is the reigning two-time Wimbledon champion and also holds the Australian Open and Masters Cup crowns.
That said, Federer is trying to become the first man to win three Grand Slams in one year since Sweden's Mats Wilander captured the Australian, French and U.S. Opens in 1988.
Up next for Federer will be the sixth-seeded Agassi, who throttled Sargsian 6-3, 6-2, 6-2 in an hour-and-a-half.
Agassi tied fellow American tennis stars Pete Sampras and Bill Tilden with his 71st U.S. Open win.
Agassi owns eight career Grand Slam titles, including U.S. Open crowns in 1994 and 1999.
He also finished as runner-up in 1990, 1995 and 2002.
Federer and Agassi have split six career matches.
Also Monday, fifth-seeded Englishman Tim Henman had to play into a fifth set before dismissing ailing German Nicolas Kiefer.
Henman was leading 3-0 in the fifth when the 19th-seeded Kiefer was forced to retire because of an injured right wrist.
ATP trainer Per Bastholt attended to Kiefer, who threw his racquet down in disgust when he realized his run was over.
Henman thus celebrated his 30th birthday with a 6-7 (5-7), 6-3, 6-1, 6-7 (4-7), 3-0 decision in 3 hours, 41 minutes.
He will appear in his first- ever U.S. Open quarter-final against 22nd-seeded Dominik Hrbaty of Slovakia.
Hrbaty was down a set and trailing Belgian Olivier Rochus 1-4 in the fourth before rebounding to win the last 11 games of the match for a stunning 2-6, 3-6, 6-3, 6-4, 6-0 decision.
Hrbaty advanced in just over 3 hours with the help of 14 aces, 47 winners and a whopping 10 service breaks.
Rochus committed 28 fewer unforced errors (77-49) and registered eight breaks, but also recorded 29 fewer winners (47-18) and was unable to hold his serve in the final set.
with files from Sports Network
