American Spieth has long rated the par-71 layout at iconic Riviera Country Club as one of his favourites while Northern Ireland's McIlroy is playing the event for the first time this year, largely because of what he has been told about the course.
Even though the notorious Los Angeles traffic makes getting to this PGA Tour venue worse than any other, that has not kept quality fields from flowing into Riviera every year, and this week's edition has attracted five players in the world's top 10.
Apart from Spieth and McIlroy, sixth-ranked Bubba Watson, his fellow American Dustin Johnson (eighth) and England's Justin Rose (seventh) will also be teeing off in Thursday's opening round on a classic layout that barely changes from year to year.
"I'm excited to be here," four-times major champion McIlroy told reporters on Wednesday after playing in the pro-am competition. "It's real strategic.
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"You've got to place your ball on the right sides of the fairways. You have to make sure you hit it to the right side of the greens. You really can't short-side yourself here, you can't really get it above the pin.
"It's a real thinker's golf course and it's a real treat to play something like this because we don't get to play them that often anymore."
Masters and U.S. Open champion Spieth, playing this week in his fourth Northern Trust Open, has made no secret of how highly he would value a first victory at Riviera.
"For me to win on a golf course that I consider one of the top few in the world, that's always a goal," said the 22-year-old Texan, who tied for fourth at Riviera last year. "It would be pretty amazing.
"This course just requires all parts of the game and a variety of ball-striking. It's an all around fantastic golf course that you don't get away with poor shots at all."
Rain swept across the heavily tree-lined Riviera layout on Wednesday afternoon but Spieth expected the course to remain firm during the tournament after being baked by unrelenting sunshine earlier this week.
"I don't think it will pour enough to change the golf course completely," said Spieth, who has recorded two top-10s in three starts on the 2015-16 PGA Tour, including victory at the Hyundai Tournament of Champions in Hawaii last month.
"I'll still plan for it to be firm. This golf course can firm up very quickly."
Spieth has been paired with fellow Americans Justin Thomas and veteran Fred Couples, a twice champion at Riviera, for the first two rounds.
In other high-profile groupings, defending champion James Hahn has been paired with Watson and Rose while Spaniard Sergio Garcia will make his first PGA Tour start of the year in the company of Australian Adam Scott and Johnson.
(Editing by Frank Pingue)
