Talk about inconvenient timing. In Sunday’s Twin Cities Marathon, Kevin Castille was running just behind the lead pack — in a group that included two-time champion Mbarak Hussein, his friend and mentor — until nature called at the 15-mile mark.

Castille rushed to the bathroom, then rushed to rejoin the chase for the men’s masters title.

“It seemed like it took me forever,’’ he said. “I didn’t think I was ever going to catch up.’’

Much to Hussein’s surprise, he did. Castille worked his way back by the 22-mile mark and pushed Hussein, who held on to win the U.S. men’s masters championship in 2 hours, 20 minutes, 20 seconds. Castille finished second in 2:20:58.

Hussein, 48, became the first man to win four U.S. masters championships. He also won the Twin Cities Marathon overall title in 2005 and 2006. Castille, a 41-year-old who is rising in the masters ranks, established a personal record in his third race at the 26.2-mile distance.

“At some point I didn’t see [Castille],’’ said Hussein, of Albuquerque, N.M. “I was comfortable. Then, all of a sudden, I look back, and he’s right behind. With his speed, I knew I was in trouble.’’

Sheri Piers of Falmouth, Maine, won her second U.S. women’s masters title in 2:38:35. Piers, 42, also won in 2011.

A quick fix

Wheelchair athlete Matthew Porterfield thought a damaged racing chair would prevent him from competing in Sunday’s marathon. An axle on the chair was bent during his flight to the Twin Cities, and when it appeared it couldn’t be fixed, he left it in the lobby of his hotel.

In the wheelers’ ranks, however, fellowship — and determination — run strong. Some other competitors, including Tyler Byers and Park Rapids native Aaron Pike, decided to try their hand at repairing Porterfield’s chair. Working in the hotel lobby, they got it ready in time for the race. Porterfield finished seventh, while Pike was second and Byers was fourth.

Joshua George, a five-time medalist at the Paralympic Games and Pike’s training partner, won his first Twin Cities Marathon title in 1:37:08.

“I’m not very mechanically inclined, but Aaron and Tyler are,’’ George said. “We’re very competitive once we get out here, but we look out for each other.’’

Cutting it close

Without the same stellar field as last year’s Medtronic Twin Cities 10-mile, Team USA Minnesota runner Jonathan Peterson wanted to find ways to self-motivate. So the night before running Sunday’s race — and winning by a strong margin — the 24-year-old shaved his reddish-blonde hair into a Mohawk.

“You have to do something funky every now and then,” Peterson said.

With less resistance than ever atop his lithe frame, the UC Davis graduate finished in 49:02. That was almost a minute over the personal-best 48:06 he ran in last year’s TC 10-mile, which was also the USA 10-mile championship and featured runners such as Mo Trafeh and Ben True.

With the difference in field in mind, Peterson — who will next run a 10-mile in Pittsburgh in November — just enjoyed the day. He fed off the clusters of early-bird spectators and enjoyed clearer skies and milder temperatures than a year ago, with enough sun to keep his newly exposed head warm.

“I was expecting it to be cold and wet, but it was beautiful out,” he said, pointing to the top of his head. “It made this work a lot better.”

Fast enough

The top three women’s 10-mile finishers all completed the race in under an hour. Minneapolis resident Laura Paulsen led the pack, finishing a minute in front of the next runner — Jillian Tholen — with a time of 58:46.

Paulsen, who is a senior innovation fellow at the Medical Devices Center of the University of Minnesota, ran the TC 10-mile for the first time last year. This time around, she was 37 seconds slower, but still achieved her goals as she trains for a California half-marathon in November.

“It’s a good, competitive atmosphere here that’s always very friendly,” Paulsen said. “I just took the lead, then tried to keep going and pretend like [the competitors directly behind her] were right on my shoulder and I had to go faster.”

Etc.

• Race officials reported that 100 runners from the marathon field and 10 from the 10-mile field were treated in the medical tent. Though 30 were sent to other medical facilities, officials said none of the conditions appeared to be life-threatening.

•  Susannah Scaroni won the women’s wheelchair division of the marathon in 1:54:37. Her time broke the course record for women’s wheelers, which was set in 1996.

• A total of 8,849 runners finished the marathon, and 8,554 finished the TC 10-mile. Both were race records during a weekend in which 24,000 people participated in events including a 5K, 10K and children’s races.