The 22-year-old Mendez flashed superb staying power, rallying in the scorching heat in the closing stage of the 1.9K swim, 90K bike, 21K run event.
"That was a hard battle," said Mendez, the reigning Xterra world champion. "I was in second place until the final 13 kms. The effort was just too hard."
From fifth in the opening swim part, Mendez worked his way up in the bike stage then outlasted his veteran rivals in the grueling run event to nail his first Ironman 70.3 victory here in 3:50:32.
Tim Reed clocked 3:52:26 to finish second while Tim Van Berkel came in third in 3:53:45 followed by five-time world champion Craig Alexander, also of Australia (3:56:24) and Bradley Weiss of South Africa (3:58:37).
While Mendez needed to unleash a strong finishing kick to snare the crown, Kahlefeldt dominated the women's pro side and completed a wire-to-wire triumph in 4:25:38.
She came out on top in the swim leg then sustained her charge in the bike and run, posting a more than 11-minute victory for her sixth career championship.
Japanese Naomi Washizu took runner-up honors in 4:36:53 while veteran Philippine triathlon champion Dimity Lee Duke settled for third in 4:39:12.
Lisa Tyack, also from Australia, clocked 4:41:01 and placed fourth in her first pro race while Kirralee Seidel, also from Down Under, timed 4:53:04 for fifth in the event held in Mindanao for the first time in a decade.
Mendez still trailed Reed in the early part of the run stage but grabbed the lead in the last seven kms and stayed ahead all the way to the finish.
"When I passed him, I never looked back," said Mendez.
Reed rued dropping his bottle of power drink off his bike in one of the humps and opted not to stop to get it back in fear of losing precious time.
"I couldn't afford to stop," said Reed who also thanked countryman Berkel for sparing a couple of power gels.
Rounding out the top 10 of the elite pros were South Africa's Bradley Weiss (3:58:37) and Kyle Buckingham (4:01:43), Australians Sam Betten (4:03:36), Eric Watson (4:13:59) and Ben Allen (4:18:08) and Canada's Brent McMahon (4:20:38).
Jorry Ycong emerged as the top Filipino finisher in the race that generated so much interest and monstrous traffic in and around the city on race day. He locked 4:24:15, followed in the Filipino elite category by August Benedicto (4:25:02), Banjo Norte (4:25:07), Jumalil Paul (4:36:24) and Benjamin Rana (4:40:42).
Other division winners in the event were Moya Johansson from Australia, who topped the 25-29 category in 4:52:00 and Great Britain’s David Watson, who topped the 35-39 group in 4:31:21.http://news.abs-cbn.com/sports/03/25/18/triathlon-mendez-kahlefeldt-rule-ironman-in-davao