It doesn’t happen often, but an air of unpredictability shrouds the Pear Blossom Run.

The 42nd edition of the 10-mile race will be Saturday, beginning in downtown Medford, and none of the dominant champions and course-record holders will toe the starting line.

Cole Watson, who in 2017 won his second straight men’s race in record time, is out.

So, too, is Max King, the seven-time champion who owned the record before Watson beat both him and his mark a year ago.

Trevor Palmer, the back-to-back men’s winner in 2014 and ‘15, will also be absent.

On the women’s side, Marci Klimek holds the course standard and won six of the past seven races, but the former Phoenix High standout won’t make it back from her Massachusetts home.

That leaves Heather Johnson, who was second to Klimek last year and has come on strong in a relatively short racing career, as the most obvious choice to prevail in the marquee event.

The 10-mile race starts at 8:20 a.m. in front of Medford City Hall. The course follows Oakdale Avenue to West Main Street and Hanley Road before returning along the same route, beginning at Ross Lane.

Other running events are the 5-kilometer road race and 1- and 2-mile Mayor’s Cup fun runs.

As of Thursday, there were 705 registered for the 10-mile, 1,185 in the 5K and 1,577 in the shorter runs — numbers similar to a year ago.

This is the second time in three years that neither the men’s or women’s champion will defend their titles. Prior to 2016, it hadn’t happened in five years.

One would have to go back to 2010 to find a similarly foggy scenario regarding favorites.

With the previous year’s winner, King, a no-show, Aron Rono — visiting his girlfriend’s family in Jacksonville — showed up out of nowhere and won going away.

The Kenyan, a 21-time NAIA All-American at Azusa Pacific University, ran what was then the third-fastest time, 49 minutes, 49 seconds, since the course changed to 10 miles in 1990.

A year later, another surprise entrant, Mike Reneau of Corvallis, gave King a spirited challenge before the latter made a late surge to victory. Reneau was a national-caliber athlete who also came in well under 50 minutes.

Whether there’s someone lurking for the 2018 who will add such lore remains to be seen.

The top returners from last year are fourth-place Neil Olsen and sixth-place Levi Jackson.

King, the former Crater High runner, has been in Portugal this week attending a rigorous running camp along mountainous trails.

Watson won the Chuckanut 50K on March 17 by more than 4 minutes and is still recovering from that, he said, with a 45-mile race — his longest yet — on the horizon.

“The Pear kind of got sandwiched between those two races I really wanted to do this year,” said Watson, a member of the U.S. mountain running team that earned the bronze medal in the world championships last summer in Premana, Italy. “I didn’t want to go out there and not be fully ready to run hard.”

Watson, who lives in Folsom, California, has turned most of his racing attention to ultras and trails while those windows of opportunity are open.

The Pear Blossom could still be in his future, said the former Rogue River High and University of Oregon runner. He set the record of 49:05 last year, bettering the mark King set in 2011 by 5 seconds.

“Yeah, definitely, whenever it makes sense,” said Watson. “I like to do it. I wanted to come back this year and I thought I’d be able to, but I’m just not ready.”

Klimek, who lives in Cambridge, Massachusetts, is running well and competing in a lot of races in New England, said her father, Rick, in a phone message.

The former Phoenix High runner on Saturday will be in an elite 5K race as part of the Boston Marathon festivities. She set the women’s Pear Blossom record of 57:04 in 2015.

Klimek had another strong race in the Pear Blossom last year, winning in 57:15. Runner-up Johnson was well back, clocking 1:01.45, but she finished more than 3 minutes ahead of her nearest chaser. Rosa Gutierrez, who was fourth last year, and Natalie Chirgwin, who was fifth, will be back Saturday as well.

Johnson is entered in the Pear for the third time, having also run in 2015.

The 22-year-old didn’t start running until after high school, doing so to combat scoliosis.

Faring well in last year’s Pear Blossom opened her eyes.

“Ever since last year, I thought, ‘Oh, OK, maybe I actually have a shot at this,’” said Johnson. “My goal is to get under an hour. If I win, that would be really cool.”

She competed in eight races last year, she said, winning all but the Pear Blossom.

In late January, she captured the Volkslaufe 25K, which served as the USA Track and Field Oregon Association championship for that distance. Her time was 1:34.35.

Reach sports editor Tim Trower at 541-776-4479 or ttrower@rosebudmedia.com.