Fraser shot three-under 69 and Allenby carded a 68 to join Chalmers at 12- under-par 276.
The trio returned to No. 18 at the Hyatt Regency Coolum and Chalmers made par to win for the fourth time on the Australasian Tour.
Chalmers had a bogey and six birdies, including back-to-back birdies at 16 and 17 to end at 12-under.
Fraser had three birdies and two bogeys through 12 holes. He birdied the 16th and 18th to get into the playoff.
Allenby was two-under for his round after 10 holes with four birdies and two bogeys. After a birdie at the par-five 15th, he birdied the last to get into the extra session.
Adam Scott (68) and Aaron Baddeley (72) shared fourth place at minus-10. Nick O'Hern (67), Marc Leishman (69) and Kyung-tae Kim (76) were one stroke back at nine-under-par 279. Kim, who led entering the final round, was the only non- Australian in the top eight on the leaderboard.
American Bubba Watson struggled to a 77 to slide into a share of 12th at minus-seven.