Simontaival scored on Finland's fifth shot after Jan Mysak had tied the shootout 1-1. Roby Jarventie had scored earlier for the Finns, and the game was ultimately decided when goalie Leevi Merilainen stopped Matyas Sapovaliv with the final shot for Czechia.
The five-minute overtime was played without a whistle and featured precious few chances. The last World Junior game to go to shots was a relegation-round game between Denmark and Belarus on 4 January 2018, some 108 games ago.
These two nations have had one of the closest rivalries in U20 history. In 38 games all time coming into today, each had won 17 and four games ended in a tie. Today was no different, a battle between two teams that had won their first games of the Group A round robin.
The Finns now have two full days off before playing Slovakia on Sunday. Czechia has a day off and then takes on hosts Canada on Saturday afternoon.
"I think we had a kind of a tough start there," offered Kasper Puutio, one of the Finnish scorers in regulation. "But I think as per our image and identity, we found a way to kind of fight us ourselves back into the game. At the end of the day, it doesn't matter how we get the win. Just finding ways to win."
"We played a great match," said Czechia's Jiri Kulich. "The shootout is just a lottery. Maybe in a soccer match we would have won."
Finland had a golden chance to get on the board soon after thanks to a terrible giveaway by Stanislav Svozil in front of his goal. He made a backpass without looking, and Aatu Raty was there to claim the errant effort. Raty made a nice deke, but Jan Bednar was that much better to keep it a 2-0 Czechia lead.
Suomi did cut the lead later in the period on a power play of its own. Jarventie snapped a one-timer past Bednar from the right faceoff dot at 16:28 to make it a 2-1 game and send Finland to the dressing room with some hope after a lacklustre period.
Indeed, the Finns came out a more determined group in the second and tied the game at 3:39. Puutio beat Bednar with a shot to the short side that was also one he should have stopped.
"It was just a pretty casual faceoff play there," Puutio explained. "I sensed there was a lot of time for me, so I just set it off the tee there and let it rip."
Czechia coach Radim Rulik challenged the play for goalie interference, but the call stood and the Czechs incurred a minor penalty as a result. Joakim Kemell wired a shot off the post during the advantage, and soon after Gabriel Szturc had a great chance short-handed but was stymied by Merilainen.
The Finns took their first lead of the game midway through the third. Aatu Raty converted a nice pass from the side of the goal by captain Roni Hirvonen, snapping a shot to the far side of Bednar. The lead lasted all of two minutes, however.
Merilainen made a sensational right pad save off an in-close chance by Michal Gut, but Gut got the puck back in front of the goal and Mysak was right there to swipe it in and tie the game, 3-3. That set the stage for extra time.