The 26-year-old carded a final-round 67 with four birdies and one bogey to finish 21 under par and claim victory by four shots at Sea Island in Georgia.

Despite holding a three-shot overnight lead, Cook was made to work hard for his first win by JJ Spaun.

The American followed a round of 62 on Saturday with a four-under-par 66, completing birdies at the sixth, seventh, ninth and 10th to move just one shot behind Cook.

But Spaun failed to continue that form and let Cook off the hook with dropped shots on the 11th and 17th.

Although Spaun birdied the last, Cook also gained shots on three of his last four holes to complete victory in style.

Spaun finished on 17 under, one shot ahead of compatriot Brian Gay, whose round of 68 featured two birdies, two bogies, a double bogey and two eagles.

Americans Brian Harman, Kevin Kisner, Andrew Landry and Chris Kirk all finished further back on 14 under.

Scotland's Russell Knox was the highest Brit on the leaderboard, on seven under, three shots above Ireland's Padraig Harrington.

Collated final-round scores & totals

(USA unless stated, par 70)

261 Austin Cook 66 62 66 67

265 J.J. Spaun 67 70 62 66

266 Brian Gay 65 64 69 68

268 Chris Kirk 63 70 64 71, Andrew Landry 70 64 67 67, Brian Harman 69 68 66 65, Kevin Kisner 67 68 65 68

269 Bud Cauley 72 63 68 66, Zach Johnson 70 68 64 67, Vaughn Taylor 67 66 68 68, Benjamin Silverman (Can) 67 67 69 66, William McGirt 70 68 65 66

270 Ted Potter, Jr. 68 68 67 67, Aaron Wise 68 69 65 68, Cheng-Tsung Pan (Tai) 68 65 70 67, Nicholas Lindheim 67 70 67 66

271 Michael Thompson 68 68 67 68, David Hearn (Can) 67 70 69 65, David Lingmerth (Swe) 68 69 67 67, Johnson Wagner 67 69 67 68, Kevin Streelman 69 68 67 67

272 Ben Martin 71 66 69 66, Brian Stuard 67 68 67 70, Kelly Kraft 70 65 68 69

273 Stewart Cink 69 69 68 67, Tyler Duncan 68 70 64 71, Blayne Barber 67 67 69 70, Tom Hoge 67 69 70 67

274 Retief Goosen (Rsa) 67 70 69 68, Martin Flores 67 72 66 69, Hudson Swafford 65 71 68 70, Sung Kang (Kor) 66 69 68 71, Matt Kuchar 69 68 68 69, Stephan Jaeger (Ger) 68 69 66 71, Brandt Snedeker 67 67 70 70, Brice Garnett 65 69 68 72

275 Trey Mullinax 70 69 66 70, Ryan Armour 69 70 71 65, Chesson Hadley 67 69 70 69, Kyung Ju Choi (Kor) 69 68 69 69, John Huh 71 68 65 71, Russell Knox (Sco) 67 70 68 70, Corey Conners (Can) 69 69 68 69, Josh Teater 68 67 70 70

276 Hunter Mahan 70 66 68 72, J.J. Henry 70 68 70 68, Patton Kizzire 66 69 70 71, Tyrone Van Aswegen (Rsa) 68 70 67 71

277 Greyson Sigg 69 67 70 71, Joel Dahmen 64 71 70 72, Chris Stroud 71 67 70 69, Nate null Lashley 67 71 70 69, Brandon Harkins 66 72 69 70

278 Brendon De Jonge (Zim) 67 67 73 71, Henrik Norlander (Swe) 68 69 67 74, Martin Laird (Sco) 70 69 70 69, Keith Mitchell 67 69 75 67, Troy Merritt 68 70 69 71, Jim Herman 67 68 71 72, Padraig Harrington (Irl) 71 67 74 66

279 Sam Ryder 68 71 68 72, Rob Oppenheim 72 66 68 73, Roberto Diaz (Mex) 70 67 70 72, Ken Duke 68 69 70 72, Braden Thornberry 72 64 69 74, Fabian Gomez (Arg) 72 66 68 73

280 Bubba Watson 71 64 76 69

281 Scott Stallings 71 68 71 71, Xinjun Zhang (Chn) 68 71 70 72

282 Beau Hossler 70 69 75 68, Cameron Percy (Aus) 69 69 67 77, Bronson Burgoon 69 68 70 75

284 Jonathan Randolph 72 67 69 76

Day three report

Rookie Austin Cook will take a three-shot lead over Chris Kirk into the final round of the RSM Classic as he chases a maiden PGA Tour title in only his 14th event.

The 26-year-old began the day with a one-shot lead but surged clear with a four-under-par 66 at Sea Island in Georgia and he is now Sky Bet's odds-on 8/13 favourite to lift the trophy on Sunday.

Cook birdied the first and second after excellent approach work and made further gains at the seventh and ninth to turn in 31.

His only blemish of the day came with a bogey on the 14th after a wayward drive was followed by a three-putt, but Cook responded with a birdied from four feet at the next.

PRICE BOOST: Austin Cook to win by four shots or more is now 9/2 from 7/2 with Sky Bet!

American Cook sits 18 under par with a round to play, three clear of compatriot Kirk (64) who is 4/1 second favourite, with Brian Gay (69) a shot further back in third and is 9/1 with Sky Bet.

Scotland's Russell Knox is the leading British contender after a round of 68 left him seven under.

Three-time major winner Padraig Harrington could only manage a 74 which left him down in 72nd on level par for the tournament.

Day two report

Rookie Austin Cook, Sky Bet's 5/2 favourite, finished his second round at eight-under 62 to put him in the lead after day two of the RSM Classic in Sea Island.

His round started well as he produced eight birdies on the Seaside Course, including four in a row between holes 13 and 16.

A long-range birdie from 34 feet on the par-4 hole one and a six-foot putt for birdie on the par-4 ninth hole helped to power him into the top spot.

SKY BET PRICE BOOST: Snedeker or Kisner to win - 8/1

The American sits just one shot ahead of his closest rival and fellow countryman Brian Gay, who shot six-under 64, while Chris Kirk, leader after day one of the event, slipped to joint third position with 70 on round two.

Scotsman Russell Knox also carded a second round of 70, putting him tied for 33rd on five under overall.

Meanwhile, former FedEx Cup champion Brandt Snedeker, playing for the first time since June after suffering a chest injury, pulled himself up the leader board to finish the round in joint sixth position.

He carded a five-under 67 on the Plantation Course, pouring in a 39-foot birdie putt on the par-4 6th hole, putting him six shots behind the pace.

Day one report

Luke Donald has withdrawn from his final event of the year after seeking medical advice for chest pains he experienced in Sea Island, Georgia.

The 39-year-old former world number one was originally in the field at the RSM Classic but, as pain in his chest grew worse across Thursday, he forfeited and sought treatment at a local hospital.

Luke Donald

England's Donald posted on his official Instagram page: "Well that wasn't quite the finish to my year I had in mind!! Had some chest pain last night and into this morning & it kept getting worse.

"After some medical advice, I had to withdraw & was shipped off to the hospital to get my heart looked at. After 7 hours of tests all looks good with my heart thankfully.

"A big thank you to the staff at the South East Georgia Brunswick hospital for taking good care of me.

"Time to put my feet up for a few weeks, recharge, regroup and get ready for a big 2018."

Donald, whose last win on the PGA Tour came in 2012, had been partnered with Brandt Snedeker and Sea Island resident Matt Kuchar for the first two rounds.

Chris Kirk is the early leader ahead of Joel Dahmen.