Injury forces seeded Baghdatis to quit
The unseeded Spadea was leading 6-2 3-1 when the fourth seeded Cypriot wildcard walked to the umpire's chair and said he could not continue.
Baghdatis had called for the trainer several times throughout the match and received treatment on the court.
American Mardy Fish also received an easy passage into the final eight, earning a walkover when Germany's Rainer Schuettler was forced to pull out of the second-round match with a stomach ailment.
Spadea will now meet Fish in the quarterfinals.
Also advancing was American Paul Goldstein who disposed of compatriot Scoville Jenkins 6-4 6-1.
Goldstein will next meet Spaniard Albert Montanes, who booked his quarterfinal place with tidy a 6-2 6-3 win over Germany's Tomas Behrend.
Spain's Fernando Vicente was a straight sets 6-2 7-5 winner over Frenchman Antony Dupuis and will take on Austrian Jurgen Melzer, who battled to a 7-6 (7-2) 6-4 decision over Brazilian Marcos Daniel.
The featured quarterfinal clash will pit top seed and defending champion Andy Roddick against another former winner and fifth seed Tommy Haas.
Results (second round):
Men’s singles
Fernando Vicente (Spain) beat Antony Dupuis (France) 6-2 7-5; Vince Spadea (U.S.) beat 4-Marcos Baghdatis (Cyprus) 6-2 3-1 (Baghdatis retired); Juergen Melzer (Austria) beat Marcos Daniel (Brazil) 7-6(2) 6-4; Mardy Fish (U.S.) beat Rainer Schuettler (Germany) W/O; Albert Montanes (Spain) beat Tomas Behrend (Germany) 6-2 6-3; 7-Paul Goldstein (U.S.) beat Scoville Jenkins (U.S.) 6-4 6-1.
SHOCK EXIT FOR HENIN
CHARLESTON: World number three, Henin-Hardenne, eliminated in the first round of her previous tournament at Miami, appeared to gain strength in her second Family Circle Cup match to reach the quarterfinals of the event she won in 2003 and 2005.
Top seed Justine Henin-Hardenne continued her Family Circle Cup dominance Thursday with a 6-4 6-4 victory over Croatian baseliner Karolina Sprem.
All the top four seeds advanced Thursday, including Russians Nadia Petrova and Svetlana Kuznetsova and Swiss Patty Schnyder.
Second seed Petrova, coming off a title at Amelia Island last week, overpowered 14th seeded Lucie Safarova of the Czech Republic 6-1 6-3 to set up a match with Colombia's Catalina Castano, the only unseeded player to reach the quarterfinals.
World number 48 Castano advanced when France's Marion Bartoli retired with left knee inflammation with Castano leading the 5-4 in the first set.
Kuznetsova, the fourth seed, overcame hip and elbow worries to defeat Lourdes Dominguez-Lino of Spain 6-2 6-1. She will play sixth seeded Anna-Lena Groenefeld, a 7-6 (3) 6-3 winner over Anabel Medina Garrigues.
Third seeded Schnyder defeated Mara Santangelo 3-6 7-6 (2) 6-3 after the Italian played brilliantly in the first set, making only eight unforced errors.
Schnyder will play France's Nathalie Dechy, the eighth seed. Dechy, finally healthy and playing some of her best tennis of the year, defeated 11th seeded Katarina Srebotnik of Slovenia 6-2 6-3.
Henin-Hardenne will face Russian Dinara Safina in the quarterfinals. Safina, the seventh seed, ousted qualifier Julia Vakulenko of the Ukraine 6-7 (6) 6-2 6-2.
Results (third round):
Women's singles:
6-Anna-Lena Groenefeld (Germany) beat 9-Anabel Medina (Spain) 7-6(3) 6-3; 2-Nadia Petrova (Russia) beat 14-Lucie Safarova (Czech Republic) 6-1 6-3; Catalina Castano (Colombia) beat 12-Marion Bartoli (France) 5-4 (Bartoli retired); 4-Svetlana Kuznetsova (Russia) beat Lourdes Dominguez (Spain) 6-2 6-1; 1-Justine Henin-Hardenne (Belgium) beat Karolina Sprem (Croatia) 6-4 6-4; 8-Nathalie Dechy (France) beat 11-Katarina Srebotnik (Slovenia) 6-2 6-3; 7-Dinara Safina (Russia) beat Julia Vakulenko (Ukraine) 6-7(6) 6-2 6-2; 3-Patty Schnyder (Switzerland) beat 16-Mara Santangelo (Italy) 3-6 7-6(2) 6-3.
VALENCIA RESULTS
Quarterfinals:
Marat Safin (Russia) beat 2-Gaston Gaudio (Argentina) 6-4 6-4; Nicolas Almagro (Spain) beat 6-Filippo Volandri (Italy) 6-4 6-1; Gilles Simon (France) beat Andreas Seppi (Italy) 7-6(2) 7-6(4).—Agencies