Aiming to become the eighth player to win back-to-back titles at the PGA Tour event, Haas squandered a three-shot overnight lead and ended up one stroke shy of joining a playoff for the tournament as he tied for third place.
The 30-year-old American had outclassed a strong field at Riviera Country Club with a flawless seven-under-par 64 on Saturday and remained in an upbeat mood after setting off birdie-bogey-birdie in the final round.
"Overall the way I played yesterday, then got off to a nice start today, made a couple of nice putts, I really felt good," four-times PGA Tour winner Haas told reporters after closing with a two-over-par 73 on a sun-splashed afternoon at Riviera.
"I didn't think I could shoot over par, and then all of a sudden to be four-over par for the day, it just kind of hit me. Every shot, I wasn't comfortable, and I didn't hit a good shot. So I deserved it."
Haas, who won last year's Northern Trust Open in a three-way playoff with fellow Americans Phil Mickelson and Keegan Bradley, was four-over for the round after he recorded his fifth bogey of the day at the par-four 13th.
Though he finished birdie-birdie to post a 10-under total of 274, he was one stroke short of joining compatriots John Merrick and Charlie Beljan in a playoff eventually won by Merrick.
"Under the gun with a three-shot lead ... maybe next time I'll handle it better but I know I'll be nervous again," said Haas. "That's part of the deal but hopefully I can handle it just one shot better.
"One shot better today I'm in a playoff and two shots better I win the tournament. There are positives to be taken but overall, you don't get this many opportunities."
Asked whether his overall performance at Riviera had given him a boost for next week's WGC-Accenture Match Play Championship in Arizona, Haas replied "Yeah, absolutely.
"Even just the last two holes there, to finish birdie-birdie puts at least somewhat of a good taste in my mouth."