His personal best when winning the last four national 800m titles is 1.47.39, while Willis is a world ranked 1500m specialist who has clocked 1.45 for the 800m trip. He is also an Olympic 1500m silver medallist.
"I'm a lot stronger now, so I'm really hoping to give him a run for his money this time around," Mathas said yesterday.
Based in Christchurch these days studying for a Bachelor of Commerce degree majoring in marketing and finance, Mathas is coached by New Zealand high performance middle-distance coach Maria Hassan.
"We've got a great team around us in Christchurch and I'm improving all the time. I came home to spend Christmas with my mother who still lives here, and to get ready for the Classic Series, although I won't be competing at the last leg in Wellington."
Mathas is getting ready for the Hunter Track Classic in Newcastle in New South Wales on January 30 where he aims to dish it out over his pet trip.
"I came second last time I was there two years ago, but I'm aiming to go one better this year. I use the Classic Series to prepare and the 800m in the Potts will be my first for the season, so I'll see where I'm at. It will be great to race against Nick again and to set the pace for yet more sub 4-minute miles at Cooks Gardens on Tuesday.
"I don't intend to run myself into the ground setting the pace. We haven't talked about it yet but I'm picking I'll be asked to run a 2.26 for the first 1km and set it up for Nick and the others. It's a good field for the men's mile and there could be four or five go under 4 minutes."
Willis wants to run a fast time as he gets ready for the world indoor championships in the United States.
American magazine Track & Field News has merit-ranked Willis eighth in the 1500m, while Athletics International has ranked him seventh after a "thin season" in the words of the panel.
Surprisingly, Willis has only previously appeared in the merit-rankings once before when third ranked in 2008. His best five marks (1500m) in 2015 were: 3:29.66, 3:35.46, 3:38.27, 3:39.31, 3:43.57.
Mathas said he was careful about what he ate on Christmas Day and avoided any second helpings of pudding.
"I'm pretty careful about my diet and luckily Christmas fell on a Friday, that's my day off. I just want to make sure I'm ready to perform well."