The home team went ahead on the quarter of an hour mark when Anderson Lopes struck on the turn from the edge of the area, giving Masaaki HIgashiguchi no chance down low to his left.
Yashuhito Endo, back in the starting line-up after three games taking it easy on the bench, then almost had an equaliser with a curling, inswinging effort that the 'keeper manger to parry away from his top corner.
A far post striker-style finish by Endo did eventually pull Gamba level just after the break - after a superb one-touch passing move on the left, and then Ademilson converted a 59th minute penalty he had earned himself when adjudged to have been taken down from behind in the area to give his team the lead.
Sanfrecce managed to earn their point after Lopes shot through a crowd of legs with four minutes to go in the 90, and the unfortunate Yosuke Ideguchi deflected it past his 'keeper when it looked covered.
Gamba then had the chance to re-take the lead and bring home three points when substitute Koki Yonekura turned briliiantly to give himself space for the shot but the home goalkeeper Hirotsugu Nakabayashi was equal to the attempt. Even then Sanfrecce's own sub - Masato Kudo had a half chance with the final kick of the match, but the shot was tame and into the welcoming hands of Higashiguchi.
Team - Higashiguchi, Oh, Miura, Kim, Fujimoto, Konno, Ideguchi, Kurata (Yokenkura, 90), Endo, Ademilson (Hwang, 75), Nagasawa (Izumisawa, 81)
47' Yasuhito ENDO