Australian triathlon star Craig Alexander has finished a narrow second place at the world 70.3 title as he prepares for next month's Hawaiian Ironman.

German Sebastian Kienle held off Alexander, the defending champion, by a minute and one second at the 1.9km swim, 90km cycle and 21.1km race in Las Vegas.

The Australian was chasing down Kienle as the temperature neared 40 degrees.

Last year, Alexander became the first Australian to win Hawaii three times as he also broke the 15-year-old course record.

Australian Melissa Hauschildt (nee Rollison) finished fourth in her title defence behind British triathlete Leanda Cave.

The Las Vegas race is half the distance of Hawaii.

Alexander was 30 seconds down after the swim, but soon joined the front group.

Kienle then took control of the bike section and led by two minutes and 49 seconds ahead of Alexander, compatriot Josh Amberger and American Andy Potts.

The German won in three hours 54 minutes and 35 seconds, beating the course record that Alexander set last year by 13 seconds.

Alexander clocked 3:55:36 and New Zealander Bevan Docherty was third in 3:56:25.

Cave also built a solid lead on the bike and held off her rivals in the run.

She won in 4:28:05, with American Kelly Williamson 1:19 back in second place.

Williamson's compatriot Heather Jackson clocked 4:32:32 for third place and Hauschildt crossed the line in 4:35:13.