The victory qualified Lee as an alternate in singles for the CIF Individual Tournament, as the top two from the league earn automatic berths.
La Cañada Coach Will Moravec said Lee played some of his best and "most relaxed tennis" Wednesday.
"His experience paid off with all the tournaments he plays and practices he puts in," Moravec said. "It's a good way for him to end the year."
Lee dominated the first set, as he varied his shots — shifting them from front, back and side to side — to keep his opponent moving, which clearly frustrated Splichal.
Splichal fell behind, 5-2, in the second set before he mounted a late charge, as he won two straight games to pull within 5-4. It forced Lee to win the next game to avoid having to win two more games and losing the set would send the match to a tiebreaker.
"I knew I just had to come back, I couldn't let him get to a tiebreaker because he was getting some confidence," Lee said. "I started tightening up my game and got more serious once he won those two games."
Lee looked to be back in control, as he won the first four points and needed just one more to clinch the game, but Splichal answered by taking the next two points.
A powerful serve set Lee up for the win, as he finished Splichal off in two strokes after Splichal barely returned the serve.
"It's like anything, you don't want your opponent to get back into the game," said Moravec, explaining the importance of Lee avoiding the tiebreaker. "It can happen in any sport — that momentum swing — where he starts getting confidence and you start losing yours."
Lee advanced to the semifinals of the league tournament with wins over South Pasadena's Eren Cameron (9-7), Temple City's Boris Law (8-3), but the sophomore met his match in top-seeded and eventual singles champion James Wade of San Marino, who Lee lost to earlier Thursday, 6-0, 6-1.