Flintridge Prep junior Hasan Doxey, who won his first Prep League championship in early May, saw his season end after he carded a 79 in the 75-player tournament. Righetti's Bobby Barajas won the tournament with a 66.
Yu, who helped the Falcons win their third consecutive league championship, said he gained experience competing in a high-profile tournament.
"In a playoff [hole], there's a little more pressure," said Yu, who finished with three birdies. "It's not an easy course, and I had a lot of mistakes.
"Everybody has disappointing days. It's a good experience, but you get used to it and then try to get better."
Crescenta Valley Coach John Pehar said Yu should become a more complete golfer next season.
"He gave his best [Monday], and he's got another chance next year," Pehar said. "Right now, he's disappointed."
Doxey, who became the second Flintridge Prep boys' golfer in three seasons to win a league title after Brett Kanda accomplished the feat in 2005, recorded two birdies.
However, Loughrie said Doxey had difficulty with his short game.
"He started out having problems with it," said Loughrie, who led the Rebels to a second-place finish in league behind Viewpoint. "He had trouble with the greens and didn't handle them well.
"That tells you what you need to go back and work on. He had some brilliant shots and learned a lot. It's a step toward him having a real good senior year."