Romaniw beat his previous record of 1:50.81, yet failed to reach the final round of competition after he was cut off while running down the homestretch.
Romaniw, a native of Canada, said that competing against such talented runners from different countries motivates him to push himself even harder in the future.
"Racing the top guys from around the world showed me how deeply competitive the sport is and how hard I have to work in the coming years to achieve my goals in the future," Romaniw said, adding that he still has "much more to give."
The only Canadian left in the competition, Romaniw ran in the second heat and finished in fifth place out of eight runners. The top two competitors from each heat advanced to the finals, along with the two runners with the next fastest times out of all three heats.
Pennsylvania State University athlete Casimir Loxsom posted the fastest time of the semifinals with a finish of 1:46.92, representing the United States. Robby Andrews of the University of Virginia, the only other American runner in the semifinals, topped Romaniw's heat with a time of 1:48.76.
Of the eight athletes who qualified for the finals, David Mutinda Mutua of Kenya finished first on Sunday, winning the competition with a personal best of 1:46.41. Loxsom and Andrews followed Mutua in second and third, respectively.
Romaniw said he had not expected to make the finals and that he was proud of his 12th-place finish.
"Although I would've liked to race in yesterday's final, it keeps me hungry knowing that there are eight guys who raced better than me," he said.
Barry Harwick, head coach of the men's track and field and cross country teams, said that he had high expectations for Romaniw based on his past races.
"He ran some very good races at home," Harwick said. "I was hoping he would make it to the semifinals and I was hoping he would run a lifetime best and he did that too."
Romaniw's journey to the World Junior Championships began after he won the 800-meter race at the Canadian Junior Nationals meet earlier in July for the second year in a row.
Romaniw qualified for the semifinals after posting a 1:51 finish in the previous round of the World Junior Championships on Friday, when he competed in the first of six heats.
The top three runners in each heat qualified for the next round, but Romaniw trailed the third-best runner in his heat by 0.08 seconds.
His time of 1:51, however, allowed him to advance since the six runners with the next fastest times from all heats also moved on to the semifinals.
Romaniw squeaked past Portugal's Jorge Batista, who finished sixth in the third heat with the same time of 1:51, for the last spot in the semifinals.
"I advanced based on the thousandth of a second or something," Romaniw said. "I actually thought I was out. Thirty minutes later, I heard the news and went crazy."
Romaniw suffered from a series of injuries during his first year at the College but never lost his competitive spirit, Harwick said.
"[Romaniw] has a lot of strengths," Harwick said. "One is that he is very competitive. Especially at a big meet, he gets very excited. He performs at a higher level even if he doesn't practice. He has a lot of natural ability."
While Romaniw said he preferred racing the 800-meter, he also has experimented with longer distance events.
"I ran the 1,500-meter about a month ago," he said. "That race is interesting because it allows more time for strategy and planning than the 800-meter."
He added that he enjoys the shorter race due to its "high intensity."
"It's a test of who can keep things under control the most when you're under extreme pain," he said.
Romaniw said he looks forward to building upon his experience at the World Junior Championships as he begins his second year on the Dartmouth track team.
Harwick emphasized that Romaniw is a "very talented athlete" and that he is excited to see what he does next year.
"I expect him to earn All-Ivy honors and he has a very good chance to advance to the NCAA championships," he said.
