Dancevic, Canada's top-ranked player, trailed 4-5 in the second set before breaking Dent's serve to get back into the match. He then broke Dent's serve the next three chances.
Dent, who won his first of four ATP Tour events on Newport's grass courts in 2002, was playing his first tour match since a pair of back surgeries last year.
"I think that I sensed he was getting a little tired in the second set,'' Dancevic said. "He hadn't played in a long time. Frankly, if he was in shape, I probably wouldn't have broken him there.''
After breaking Dent to even the second set 5-all, Dancevic held serve before closing out the second set with a well-placed forehand passing shot. He broke again in the second and fourth games of the final set - a stretch where he won eight straight games - before Dent finally held serve in the sixth game.
Dancevic failed on four match points in the sixth game before closing it out when Dent hit a backhand return into the net on the fifth match point.
"I don't think he's played that long (in his comeback),'' Dancevic said. "If he did, it wouldn't take him long to play well again.''
Dent, 27, who reached No. 21 in the world in 2005, was given a late wild-card entry into Newport. He wasn't that surprised by the result.
"It was to be expected,'' said Dent, who had surgery last March and September. "I was told a year ago there was no way I was playing tennis and I'm up a break on the (No. 7) seed in the tournament. It was tough to fail the way I did, but it's all part of the process.''
Dent said the original injury was "a broken vertebrae on both sides.''
Five players that are rated the top players in their respective countries played in Newport in the past two days.
In other first-round play, fifth-seeded John Isner beat Jesse Levine, 6-3, 6-1; eighth-seed Kevin Anderson, South Africa's top-ranked player, beat Gilles Muller, the top rated player from Luxembourg, 6-7 (3), 6-3, 6-3; Pakistan's top player, Aisam-Ul-Haq Qureshi defeated Benjamin Becker, 7-5, 7-6 (5); and Prakash Amritraj edged Joseph Sirianni, 6-7 (3), 6-4, 6-4.
Top-seeded Mardy Fish was slated to play his first match on Wednesday. A top seed has never won the title in the tourney's 31-year history.
The Hall of Fame Championships is played in conjunction with the annual induction ceremony, which will be held on Saturday. Michael Chang, the 1989 French Open champion, heads this year's class. Contributors Mark McCormack and Eugene Scott, both posthumously, will also be enshrined.
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