Weekley was three strokes behind leader Scott Stallings after seven holes before knocking in a short birdie putt at the eighth, then followed with an 18-footer for birdie at the ninth to get within one at 12-under.
As Stallings tripped to a double-bogey at the 15th, Weekley birdied the 10th to claim a 2-stroke lead and added another gain at the 13th. He would par his final five holes to hang on for the victory and collect his third career win on the PGA Tour.
Weekley returns to defend his title against a field that includes 10 of the top 25 players in the world.
Among that group is newly-crowned world No. 1 Adam Scott, who will make his first appearance as the top-ranked player in the world.
Each of the past five Colonial winners have come from behind on the final day to claim the title.
Golf Channel will have full television coverage the first two days and early action on the weekend before handing off to NBC.
The PGA Tour travels to Ohio next week for the Memorial, where Matt Kuchar collected his sixth career PGA Tour win and second victory of the season last year.
BMW PGA CHAMPIONSHIP, Wentworth Club, Surrey, England -- The European Tour moves to England this week for the flagship event on tour, the BMW PGA Championship.
Matteo Manassero birdied the fourth playoff hole last year to top Simon Khan and Marc Warren, earning his fourth career win in the process.
With the victory, Manassero became the youngest winner of the event at 20 years old.
Warren was eliminated from the playoff on the first extra hole following an errant drive and then a water hazard. Manassero and Khan would both birdie the hole to move on, and traded pars at the second playoff and birdies at the third.
Khan then found the same stream as Warren in the fourth extra hole and Manassero took advantage by finding the green with his approach and 2-putting for the win.
This year's event will be the 60th anniversary of the tournament and will see 10 major winners in the field, including the PGA Tour's Players Championship winner Martin Kaymer.
Also in the field will be all but one of Europe's victorious 2012 Ryder Cup team. The only player who will not be participating is Graeme McDowell, who will remain home to be with his pregnant wife.
Along with Manassero, other former winners in the field will be Miguel Angel Jimenez, Luke Donald, Simon Khan, David Howell, Scott Drummond and Jose Maria Olazabal.
Golf Channel will have coverage of all four rounds.
The European Tour heads to Sweden next week for the Nordea Masters, which Mikko Ilonen won last year for the second time.
AIRBUS LPGA CLASSIC, Robert Trent Jones Golf Trail at Magnolia Grove, Mobile, Alabama -- The LPGA Tour travels to Alabama this week for the Airbus LPGA Classic.
Last year, Jennifer Johnson collected her first career victory at a record- setting 21-under-par 267. Her mark bested the previous record by four strokes.
Johnson came from behind to win that title with a 7-under 65 in the final round, topping Pornanong Phatlum and Jessica Korda by a shot.
Johnson, Phatlum and Korda will all return this year and will compete against a field that also includes former winners Stacy Lewis (2012), Se Ri Pak (2010) and Angela Stanford (2008).
Also playing this week will be 2014 winners Michelle Wie, Paula Creamer, Lexi Thompson, Karrie Webb and Anna Nordqvist.
Golf Channel will have tape-delayed coverage of the first two rounds before carrying live action on the weekend.
The tour moves north to New Jersey next week for the Mobile Bay LPGA Classic, where Webb battled windy conditions to earn her 39th career victory and snap a two-year winless streak.
SENIOR PGA CHAMPIONSHIP, The Golf Club at Harbor Shores, Benton Harbor, Michigan -- The Champions Tour shifts to Michigan this week for its second straight major, the Senior PGA Championship.
Kohki Idoki came from relative obscurity, and five shots back, at this event last year to win in just his second career Champions Tour start.
The Japan native carded a 6-under 65 during the final round to best Kenny Perry and Jay Haas by two strokes.
Idoki returns this year and will try to derail Perry's bid to win a fourth straight major.
Perry won the Regions Tradition last week to go along with wins at the Senior Players Championship and U.S. Senior Open last year.
The 75th staging of the event will also include Bernhard Langer, Colin Montgomery, Mark Calcavecchia and Steve Elkington.
Golf Channel will have television coverage of the first two days and early on Saturday before handing off to NBC for the remainder of the tournament.
The Champions Tour moves to Iowa next week for the Principal Charity Classic. Russ Cochran claimed that title last year for his fourth Champions Tour victory.
REX HOSPITAL OPEN, Midland Country Club, Midland Texas -- The Web.com travels to Texas this week for the Rex Hospital Open at Midland Country Club.
Last year, Chesson Hadley birdied five of his last eight holes to rally for a 2-stroke victory over Danny Lee.
Chesson Hadley has since moved on to the PGA Tour, so he will not return to defend his title.
Previous winners this season Alex Cejka, Adam Hadwin, Jon Curran, Carlos Ortiz, Kris Blanks, Andrew Putnam and Max Homa will be on hand. The only 2014 winner not competing is Blayne Barber.
Ortiz is seeking an immediate promotion to the PGA Tour with his third win of the season.
There will be no coverage of this event.
The Web.com Tour will have next week off before returning for the Cleveland Open, which is a new event.