The three-way battle to compete in the SEA Games men's marathon is set to heat up over the next two months.

Defending champion Soh Rui Yong, who easily met the SEA Games qualifying mark when he clocked 2hr 24min 55sec at the Chicago Marathon in October, will attempt to seal his entry into the biennial Games by running in the Kagawa Marugame International Half Marathon today.

The qualifying time for August's SEA Games in Kuala Lumpur is 2:37:10, pegged to the bronze-medal timing of the 2015 Games.

Singapore Athletics' (SA) 2017 SEA Games selection criteria, however, state that athletes who qualified between Aug 1 and Dec 31 last year must do a "performance test" in any SA-sanctioned competition this year from Jan 1 to May 31.

To cement his spot in the SEA Games men's marathon, Soh must either clock 1:12:30 in a half marathon, or 32min 57sec in a 10km race during this period.

Meanwhile, 2013 SEA Games champion Mok Ying Ren and fellow national marathoner Ashley Liew, eighth in 2015 in Singapore, are also gunning for qualification.

Mok - whose personal-best timing is 2:26:30, set in 2013 -is set to take part in next month's Seoul International Marathon, while Liew will compete in the Tokyo Marathon on Feb 26.

While Soh is "pretty confident" of meeting the half-marathon mark, he said: "I'm taking nothing for granted. Anything can happen in road racing; it's less predictable than being on the track."

The 25-year-old emphasised that his target for the SEA Games is to retain the gold medal, adding: "The time, how many steps I take, and what my hair looks like at the finish - those are all secondary."

Liew, 30, is also confident of meeting the SEA Games qualifying mark in Tokyo, pointing to his 2:38:39 effort at September's Berlin Marathon as a big reason.

"The weekend of that race was my last week of school, so it wasn't the most ideal of preparations," he said. "But even then I could run 2hr 38min, so now that I've settled into my current work and training routine, I'm quite confident of meeting the SEA Games qualifying time."

Liew, who works at the Family Health Chiropractic Clinic, added that his target for the Tokyo Marathon is to improve on his personal best of 2:32:12, which was set in New Orleans in 2015.

According to SA's website, the national sports association (NSA) will select a maximum of two athletes for each individual event.

The Sunday Times confirmed with SA president Ho Mun Cheong that if more than two athletes qualify, the two with the fastest timings will be selected.

Asked about the NSA's target for the SEA Games, however, he said: "It's still too early to talk about targets as we're still in the qualifying window period.

"We have some (medal hopefuls) in mind, but we'll have a better idea in about two months' time."