Adding to a bulging curriculum vitae is one thing but more significant is how Willis has done it. The 31-year-old looks close to matching the form which saw him cannon to the 2008 Olympic podium in the 1500m.
One example came during the race Willis described as a "bucket list achievement", running 3m 49.83s for the mile. He looked serene settling into the pack to conserve energy and avoid spikes. There was no panic as he looped the track before the final straight. Then came the determination in the finishing straight where he escaped disappointment by 0.17s. Exhaustion and elation took hold as the impact of his feat dawned and he clambered to shake the hand of race winner Ayanleh Souleiman.
A renowned student of the sport, Willis has returned to Michigan to prepare for the 1500m-5000m double at the Glasgow Commonwealth Games. No athlete has won both events since they were installed as metric measurements in 1970 (Kenya's Kip Keino won the empirical equivalents of one and three miles at Kingston in 1966).
"I always wanted to give the 5k an honest go [at the Commonwealth Games]," Willis says. "In the past, I didn't think my body could withstand the training, but I am reaping the rewards of consistent health.
"I have slowly increased the volume of miles in my legs in Arthur Lydiard fashion. I've come across that plateau where I don't feel tired after successive days of running up to two hours a day. I've never had the chance to do that.
"It's a bit like a rugby player having a go at league. You do similar training but it involves a different execution of skills in competition. The 5000m involves a different sort of fatigue. Your body is tired but you can still sprint at the end because you haven't built up the same lactic acid compared to a 1500m when they're like lead."
The 5000m field will feature two of the discipline's best exponents in Olympic and world champion Mo Farah (England) and world indoor 3000m champion Caleb Ndiku (Kenya), who beat Willis in Ostrava.
"The depth drops off after that," Willis says. "It's a chance to race those top guys without being as concerned about a cluster of others. I also wouldn't want to give up an opportunity to race Farah in the UK with a packed crowd going nuts."
Regard-less of the prospect, breaking the 3m 50s-mile barrier might be the highlight of Willis' season. It'll certainly be a highlight of his career.
"The Commonwealth Games means a lot but I've already won a gold [in the 1500m in 2006) and a bronze [in 2010]. I could sleep easily at the end of my career if I didn't pick up another medal but missing a chance to break the 3m 50s barrier would've left me frustrated. It feels like part of my career is now complete.
"There's really only one to two races a year when you have a chance to go after a time like that, and they're in May and June when you're generally only racing at 85-90 per cent of your peak, heading into the rest of the season. If you can do it, that's great, but you can't afford to put all your eggs into that basket."
Willis' wellbeing has coincided with a change in lifestyle after the arrival of son Lachlan on American Independence Day last year.
"He shapes our decision-making and brings structure to our days," says Willis, who will train at home until heading to Glasgow in mid-July. "Although I'm a full-time professional athlete, I also consider myself a full-time stay-at-home dad alongside my wife who's a stay-at-home mum.
"We've also formed Team Willis Events to organise a professional track meet on August 10 which we've called the Michigan Track Classic. It's been an awesome exercise to see if we can work well together. You never know how well things will go once kids come into the picture but it's only strengthened our marriage."
Willis says the idea was spawned last year when he was trying to organise a race during an injury-hampered world championships build-up.
"In a fortnight, we put on a race at our local high school for a bunch of guys who wanted to break four minutes for the mile. We ended up with 4000 people coming. The community support blew us away.
"We thought it'd be a wasted opportunity not to turn it into a more formalised event. Hopefully it's an opportunity for me to run fast without having to travel because it's just down the street. Nothing makes you more nervous than putting on an event and wondering if the crowd will attend to cover your expenses. When they do, it gives you a real rush, like playing sport itself."
