Australian triathlete Pete Jacobs allayed concerns about his form for his Ironman world championship defence with a dominant victory in Sunday's half Ironman on Queensland's Sunshine Coast.

Four weeks out from the big race in Kona, Hawaii, Jacobs led after each leg of the 1.9km swim, 90km bike and 21.1km run to clock a classy 3h39m58s and win by about seven minutes from countrymen Clayton Fetell (3:47.07) and Casey Munro (3:50.58).

Jacobs was delighted with his victory in Mooloolaba, especially after some below-par race results this year had many questioning whether he could back up his world championship on October 12.

"I said that I was burning to get a win here," said Jacobs.

"I'm getting in good shape to defend my title at Hawaii, and I felt awesome on the bike and built into the run.

"I have worked on my bike and strength and it's all going to plan for Hawaii."

Kiwi super mum Gina Crawford was similarly buoyed for her Ironman world championship bid after wining the women's race in 4:23.17 despite problems with a flat tyre on her bike.

Crawford had to dig deep during the run leg to secure victory by 59s from Japan's Kiyomi Niwata while Australian Lisa Marangon came third (4:33.16).

"Kiyomi caught me at 10km and I didn't think I could win, but it's a big sacrifice for me to come here and race and be away from my son for three days so I wanted to win it for him, I gutsed it out and got the win," Crawford said.

Crawford spent the swim and bike as the hunter chasing Marangon who built a 3min plus lead on the back of a strong swim-bike combination.

After taking the lead early in the run she became the hunted as triple Olympian Niwata produced a blistering fast run to move into contention.

Crawford made a move in the late stages building a 37sec lead, and was able to hold on for the win.

"I had an issue with my bike, the tyre was flat and I couldn't pump it up and ran out of time so I just left it," said Crawford.

On the ride I was working hard but not really getting anywhere, I was surprised I ran so well, and glad I gutsed it out and got the win.