Follow The Athletic’s French Open coverageWelcome to the French Open briefing, where The Athletic will explain the stories behind the stories on each day of the tournament.On Day 12, the women’s semifinals arrived, with all four players in search of their first appearance in a Grand Slam final.How did a nervy start determine the trajectory of almost an entire match?Tennis matches are never usually decided in the first two games, but they can dictate the direction of travel.It was Marta Kostyuk who seemed nervous on Court Philippe-Chatrier Thursday afternoon, during the opening game of her first Grand Slam singles semifinal against Mirra Andreeva.The Ukrainian No. 15 seed served two double faults, gifting an easy break for Andreeva, who was playing in only her second Grand Slam semifinal. But the Russian No. 8 seed showed her own nerves in her service game, double-faulting once and trailing 0-40 to give Kostyuk an immediate opportunity to reset the match.But Kostyuk made three consecutive errors, letting Andreeva claw her way back to deuce. A point later, she pulled out an ace to hold serve and lead 2-0. It was a Sliding Doors moment.Had Kostyuk broken back to level the score at 1-1, she could have treated that first service game as if it had never happened, wiped the slate clean mentally and moved on. But losing the first two games when Kostyuk really should not have done — first because she was serving and then when Andreeva was 0-40 down — set the tone.“I didn’t start the best, but, you know, it happens,” the 23-year-old said in her news conference. “…I was missing more. Obviously felt pressure…The serve was not great for me today. I was rushing a lot, and just, a bit more chaotic.”Andreeva, ranked No. 8 in the world, took the momentum and ran with it, racing to a healthy 4-0 advantage and eventually taking the first set for the loss of just one game, to set up a 6-1, 6-3 win.“If I get nervous when I serve, I think: ‘She also can get nervous when she serves,'” Andreeva, 19, said in her press conference. She has been working on her concentration and visualization process to the extent that she said she could see the individual hairs on the ball throughout the match.A similar situation which dictated the rest of the match occurred in last year’s Wimbledon final, when American Amanda Anisimova, trailing 2-0, could not convert one of the four game points in her second service game against world No. 2 Iga Świątek.Had she done so, she would have at least got on the scoreboard, albeit still a break of serve down, and given Świątek something to worry about. Instead, the four-time French Open champion ran away with the set, ultimately double-bageling Anisimova to win her maiden Wimbledon title.