Hint: It involves working together.

They share a coach, have a combined total of more than two dozen national titles, and are the first- and second-fastest half marathoners in U.S. history. And on Sunday, for the first time, Molly Huddle and Emily Sisson will line up together at the London Marathon to race one of the fastest 26.2-mile courses in the world.

It is Huddle’s fourth crack at the distance and Sisson’s debut, but they plan to utilize some teamwork in a deep international field that’s likely to splinter early in the race. The duo is coached by Ray Treacy, women’s cross-country coach at Providence College.

“Obviously a lot can happen in the marathon, so we’re aiming for the ideal situation,” Huddle said during a phone interview on Monday. “But Ray does think we’ll be able to work together for a lot of the race and finish pretty close together, too. We both made it to the start line ready to roll, basically.”

Huddle, the two-time Olympian and American record holder in the half marathon (1:07:25) and 10,000 meters (30:13:17), enters London with a marathon best of 2:26:44 from her fourth-place finish at the 2018 New York City Marathon. Her goal on Sunday is to improve that PR and gain more experience at the distance before competing at the 2020 U.S. Olympic Marathon Trials in Atlanta next February.

After two tries in New York (she was third in her 2016 debut) and one shot at Boston in 2018 (when she experienced symptoms of hypothermia), Huddle is eager for an opportunity to focus on time, rather than strategy and tactics. Given a perfect day, she’ll aim to break 2:24, she said.

“It’s kind of the last chance to run a fast time on a fast course for me before the trials—and maybe ever, because I’ll be getting pretty old after the trials and before the Olympics,” said Huddle, who is 34. “It’s an opportunity I won’t have many more of—I have a sense of urgency. It gets me a little more motivated.”

The objectives are a little different for Sisson, 27, because she’s never raced a marathon before—though her performances during the buildup show promise. At the Houston Half Marathon in January, she finished in 1:07:30, just five seconds off Huddle’s American record. And at the Stanford Invitational in March, she walked away from the track with a 36-second personal record in the 10,000 meters, clocking 30:49:57.

“I’m trying [the marathon] now because it gives me the option of what to focus on next year. If it goes well, I can kind of decide if I want to try both [the 10,000 meters and marathon] at the Olympic Trials,” Sisson said, during a phone interview on Tuesday. “If it doesn’t go well, then I’ll just go back to the 10K and when the timing’s better, I’ll move up to the marathon.”

Although Huddle and Sisson consider themselves training partners, their schedules didn’t match up for workouts and long runs. In fact, Tuesday in London was the first time in their marathon buildup that they completed a speed session together. Sisson started three months ago from a different point because of the half marathon in Houston, while Huddle was aiming for a fast 10,000 meters in March (mission accomplished: she finished in 30:58.46).

Sisson also said that her strength is tempo workouts, while Huddle spends more time on track intervals.

“Track work can beat me up a lot, so I think that’s why we weren’t put together during workouts,” Sisson said. “It still helps a ton just having Molly there to go for easy runs so I can bounce ideas off of her or plan trips like heading to London, or meeting up for dinner. It makes it a lot less lonely.”

Sisson and her husband, Shane Quinn, have permanently relocated from Providence, Rhode Island, to Scottsdale, Arizona, to take advantage of the warm winters, proximity to high altitude in Flagstaff, and to John Ball, a chiropractor who treats many professional runners from his office in the Phoenix area. Huddle and her husband, Kurt Benninger, are based in Arizona for much of the year as well.

Their training has averaged around 115 miles per week, Sisson estimated. For Huddle, it’s a slight decrease in volume—an adjustment based on how she felt at the end of previous marathon cycles. But she’s equally grateful to have Sisson by her side this weekend.

“At Stanford I don’t think I would have been able to run under 31 minutes if I didn’t have Emily there pacing and knowing we do the same training—I know what we’re prepared to do,” she said. “With the depth of the London Marathon, we’ll eventually fall off the pack and it’s good to know we’ll be able to run together.”

London’s professional field features six women who have run faster than 2:20, including Mary Keitany of Kenya, who set the world record for a women’s-only race (not paced by men) in 2017, finishing London in 2:17:01. And Vivian Cheruiyot, also from Kenya, is back to defend her title.

If the vet Huddle dispenses any wisdom to the rookie Sisson on the starting line, it’ll likely be to practice patience.

“This is the best of the field, which is new even to me, so I would maybe just remind her, ‘We gotta be careful here,’” Huddle said. “We have each other, so if we have to let people go early, that’s okay. We have to stay pretty calm if it’s fast.”

The gun goes off for the women at 4:24 a.m. Eastern on Sunday. NBCSN and NBC Sports Gold will begin broadcasts at 4 a.m. Eastern. On the men’s side, Kenyan Eliud Kipchoge lines up for his first 26.2 miles since setting the world record in Berlin (2:01:39), as well as Mo Farah, the four-time Olympic gold medalist who won the Chicago Marathon in October.