Gardiner has played well enough in this four-tournament series that determines PGA Tour cards that he already has locked up his return to the big leagues. A win in the final event would give him top status for the 2013-14 season and a spot in The Players Championship.
Hadley, who also has secured his card through Web.com Tour regular-season money list, had a two-shot lead for most of the third round on the Valley Course at the TPC Sawgrass. But he bogeyed the 17th, and then took double-bogey on the last hole for a 70 that left him one shot behind with Joe Durant (68).
Gardiner was at 10-under 200.
The Web.com Tour Finals replaces the old version of Q-school, which finished with a six-round tournament. The top 25 from the Web.com Tour regular season are assured their PGA Tour cards, leaving 25 additional cards based on a special money list from the four tournaments.
Durant was among a dozen or so players who go into the final round with a shot at getting one of those 25 cards.
Andrew Putnam, whose older brother won the money title on the Web.com Tour and is assured top status, made a hole-in-one on the tough 11th hole on his way to a 67 and was in fourth place. He likely would need to finish around 15th to get his card.
Others who made big moves in the third were Andrew Loupe (67), Rod Pampling (68) and Russell Knox (68), who were tied for sixth at 6-under 204. Chad Campbell, who played on three Ryder Cup teams, had a 67 and was among those at 5-under 205.
Campbell is just on the outside of getting one of the 25 cards and would need another solid round Sunday. Ben Kohles also was at 205, but because he started much higher on the special money list, he wouldn't need to do as much in the final round.
Alexander Rocha of Brazil also was on the cusp of a card until making bogey on half of his holes for a 78 that took him out of contention.
Gardiner made the cut in only seven of 23 events he played in his rookie season on the PGA Tour. But he tied for third in the first event of the Web.com Tour Finals and came into the final event at No. 11 on the money list.