Australian runner David McNeill has almost certainly claimed the third and final spot in the men's 5000m for the London Olympics after smashing his personal best at a meet in California.

McNeill finished third behind Canadian winner Cameron Levins at the Mt Sac Relays in Modesto in a time of 13 minutes 19.31 seconds, stripping six seconds off his personal best.

The effort also moved the 25-year-old Victorian up to eighth on the Australian all-time list.

And even more importantly, the time was less than a second under the Olympic qualifying standard of 13:20.

Craig Mottram and Collis Birmingham have already been selected to run the 5000m in London and they are now likely to be joined by McNeill, who bounced back from a disappointing showing at last month's Australian Olympic trials in Melbourne.

"I just can't believe it," McNeill said.

"A month ago I ran 14:40. It's just a shock."

McNeill will shift his focus to his favoured 10,000m at next week's Prefontaine Classic in Eugene, Oregon.

Fellow Australian Eloise Wellings also gave her Olympic selection hopes a lift by clocking 15:20.67 to finish second in the women's 5000m in Modesto.

It strengthens Wellings' case to be picked to run the 10,000m in London, the distance where she has previously bettered the A standard.

Marathon:

Australian runners Martin Dent and Scott Westcott have missed out on recording an Olympic qualifying time in the London marathon.

Dent and Westcott were looking to join compatriot Michael Shelley by running under the Olympic A qualifying standard of 2 hours and 12 minutes before the London Games start on July 27.

Dent finished the race in 21st placed in a time of 2:17.32 while Westcott came home in 32nd spot in 2:22.16.

AAP