The 2-1 defeat to Jubilo Iwata condemned the 2008 Champions League winners to the second tier next season along with Vissel Kobe and Consadole Sapporo.
Yuki Kobayashi scored a late winner for Jubilo to send the visitors down.
Gamba's Shu Kurata had cancelled Ryoichi Maeda's opener before Kobayashi got the winner with five minutes to go.
Sanfrecce Hiroshima rounded off their J.League championship winning season by stretching their final advantage to seven points in the table with a 1-0 win over Vissel Kobe who were relegated as a result.
Sanfrecce, who had clinched the title last weekend, finished the league season in style as second-placed Vegalta Sendai were thrashed 6-2 by mid-table FC Tokyo.
Sanfrecce moved to 64 points as Koji Morisaki scored the only goal from the penalty spot after 52 minutes, a defeat which saw the Kobe side demoted to the J.League's second division.
Two late goals from Nemanja Vucicevic rounded off Tokyo's emphatic win, netting in the 82nd and 90th minutes.
Lucas (8 and 17), Hyun-Soo jang (49) and Kazuma Watanabe (56) got the other goals for the home side.
Shingo Akamine (35) and Yuki Muto (90) were on target for the visitors.
Urawa Red Diamonds finished the campaign in third with a 2-0 win over Kashima Antlers with goals from Yosuke Kashiwagi (23) and Tomoaki Makino (59).
Yokohama F. Marinos moved above Sagan Tosu into fourth with a 1-0 win against Sagan with Shunsuke Nakamura scoring the winner after 53 minutes.
Kashiwa Reysol had to settle for sixth in the final table following a 2-0 away defeat to Kashima Antlers whose goals came from a Yuya Osaka double after 41 and 58 minutes.
Bruno Lopes scored twice and there were also goals from Shusuke Tsubouchi and Alan Mineiro as Albirex Niigata defeated the already relegated Consadole Sapporo 4-0.
Tomonobu Yokoyama scored two goals in the second half, both of them equalisers, as Cerezo Osaka earned a 2-2 draw against Kawasaki Frontale.
The visitors led twice through Kengo Nakamura and Yu Kobayashi but each time Yokoyama was on hand to level matters.
The game between Shimizu S-Pulse and Omiya Ardija finished 0-0.