After Daly had stolen the thunder early in the day by firing a bogey-free 67, Fernandez-Castano produced a late charge to overtake him with a birdie on the last hole to set himself up nicely for the tournament.
Korean K.J. Choi and Australian Jason Day were in joint third place on 68 while former winner Paul Lawrie was in a bunch of five players a further shot behind on 69.
Yet, the top two couldn't have played more contrasting rounds.
While Daly was almost blemishless as a sandstorm ravaged the course, Fernandez-Castano's game was a mixed bag and the Spaniard must have left the course with a feeling of what could have been if he hadn't had those bogeys to go with his nine birdies.
But Fernandez-Castano would have to surrender the headlines to Daly, who gave a rare glimpse of his abundant natural talent in "brutal" conditions.
Looking much trimmer now, Daly, wearing colourful trousers and sporting a stubble, began steadily by parring his first two holes before picking up a shot on the next. He then stroked two more birdies before the turn even as the wind picked up.
A further two more birdies over the final three holes put the former US PGA Championship and British Open winner in a solid position to launch his bid to become the first American to win the tournament.
"It's one of the best rounds I've ever played in a wind like that," the 45-year-old said. "It was brutal. I mean I'm pretty shocked myself shooting five-under.
"I've had five and a half weeks off and didn't touch the clubs much, so being the first tournament of the year I am really happy."
Daly added that he felt like wearing a mask on the course.
"You really do. It's weird, you just feel like you are eating a lot of sand."
Daly said he was in no mood to practice on Thursday after finishing his round before noon. "I don't feel like eating more sand. Hopefully I'll lie down a bit. It's hard to work on your game in conditions like these."
Daly won the 1995 Open Championship at St. Andrews in similarly windy conditions -- without the sand, though -- but his last victory came eight years ago at the 2004 Buick Invitational.
Even that victory was his first in nine years on the US PGA Tour after which he rapidly went down and is now placed 543rd in the Official World Golf Ranking.
Big-hitting Alvaro Quiros, the 2009 champion, also looked in good form when he picked up shots over the first two holes but a double bogey on the eighth and two more bogeys later in the round saw him finish his first round at a level-par 72.
Defending champion Tomas Bjorn of Denmark had a nightmare first round 79, while former champions Henrik Stenson and Rolf Muntz fared much worse, shooting 81 and 82 respectively.
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