The trio top a bunched leaderboard after reaching four under par at The Celtic Manor Resort on Thursday afternoon, with the host course showing its teeth on day one.
Guerrier displayed impressive fighting spirit, recovering from a hat-trick of early bogeys to grab a share of the lead, while Syme briefly got to five under before dropping a shot at his closing hole, and Whitnell made four birdies and no bogeys.
Ewen Ferguson, Maximilian Kieffer, Eddie Pepperell, Marcus Armitage, Mikko Korhonen and Ivan Cantero Gutierrez were one shot back in a tie for fourth.
The day will live long in the memory of David Howell, who became just the third player to make 700 DP World Tour appearances.
Guerrier started at the 11th tee in the afternoon and opened his round with a birdie from six feet but he followed that up with three successive bogeys to slip to two over par.
The Frenchman bounced back in style, though, making back-to-back birdies from around eight feet at the 15th and 16th before picking up another shot from close range on the 18th to repair the damage.
Guerrier sent his tee-shot at the short third to six feet before holing the birdie putt to get to two under.
He holed from 25 feet for another birdie at the fifth before rolling in another lengthy putt on the ninth green to head into the clubhouse on four under.
After his round, Guerrier said: "You need to hit a lot of good shots to be in contention this week, and I did today so I’m really happy.
"My irons were good, I had a lot of opportunities so I’m happy today."
Scotland's Syme started well, birdieing the 11th - his opening hole - from nine feet before draining a monster putt at the 14th to climb to two under.
He made it back-to-back birdies from close range on the 15th and closed his front nine with a fourth birdie of the day at the first.
After a run of seven straight pars, which included a good save at the seventh, Syme picked up another shot on the ninth to take the solo lead on five under.
But he finished the round with his only bogey of the day at the tenth to drop back to four under.
Syme said: "Overall I’m pleased, I kept my ball out of the trouble well and it’s a good start.
"You’ve got to drive it well and the greens are pretty undulating in parts as well so you need to be cautious about where you’re leaving it.
"It challenges every part of your game, all round you need to play really good golf to score, it’s just a challenging golf course."
Whitnell opened his birdie account at the sixth with a 15-footer before taking advantage of the par-five ninth and 11th.
He continued to create birdie chances but did not add to his tally until the 16th, where he holed from five feet to join the co-leaders on four under before parring his way home.
Whitnell said: "It’s tough out there, the wind is swirling about which is making it extremely tough but I had a game plan and managed to execute it today.
"There are obviously tough holes out there so I just tried to be disciplined. Gordy has been great on the bag this week so we made some great decisions and I managed to execute the shots that I needed to.
"I just need to keep doing what I’m doing tomorrow, keep grounded and try and clip off a few birdies here and there."