Unbeaten Vegalta looked on course to make it eight wins from nine at the start of the new campaign when Shingo Tomita put them ahead in the 19th minute, but hosts Sagan levelled just before the hour-mark through Yohei Toyoda to claim a point.
Despite the draw, Vegalta still boast a five-point lead at the summit over Shimizu S-Pulse, who moved up to second with a 3-0 home win over Kashima Antlers, Sho Ito (five minutes), Toshiyuki Takagi (72) and Genki Omae (75) netting the goals.
Kashima replaced Sanfrecce Hiroshima, who dropped to third after surprisingly going down to a solitary second-half goal from Naoya Kikuchi at home to Albirex Niigata, who were left celebrating only their second win of the season.
Fourth-placed Urawa Red Diamonds also suffered defeat as they lost 2-1 at home to Yokohama F. Marinos.
Urawa appeared to have salvaged a point when Tomoaki Makino struck 12 minutes from time to cancel out Manabu Saito's 12th-minute opener for the visitors, but Marcos Marquinhos popped up with two minutes to go to earn Marinos the points.
Bottom side Consadole Sapporo picked up their first win of the season after beating mid-table Cerezo Osaka 1-0 thanks to Yusuke Kondo's 25th-minute goal, while Vissel Kobe downed Omiya Ardija 3-0 with strikes from Keijiro Ogawa (three), Lee Seon (60) and Hiroto Mogi (68).
The other match saw Kawasaki Frontale hold off a Jubilo Iwata fightback to claim a seven-goal thriller 4-3.
Kawasaki's goals came from Ryota Oshima (30), Takuro Yajima (53, pen & 62) and Yusuke Tanaka (55) but Jubilo pushed their opponents to the end with efforts from Kosuke Yamamoto (59 & 67) and Yoshiro Abe (90).