Shinji Okazaki put Mainz in front after 33 minutes with his 26th goal in the German top flight - equalling the record for a Japanese player.

Paderborn's Elias Kachunga smashed home four minutes later to bring the home side level and Uwe Hunemeier's header put them ahead with three minutes left.

But the Paderborn captain then conceded a penalty with time almost up, which South Korean midfielder Koo calmly stroked into the corner.

"Towards the end we had chances to keep the ball better," Paderborn manager Andre Breitenreiter said. "We were bitterly punished for not doing so.

"But it says it all that we're disappointed not to have won. We deserved to."

Close to 15,000 supporters had packed into the Benteler Arena to watch Paderborn become the 53rd team to play in the Bundesliga.

Mainz, who finished seventh in the top flight last season, dominated possession in the first half and Koo finally got a shot on target after the half hour.

A minute later, Johannes Geis saw a dipping free-kick come back off the post but Okazaki, who top scored for Mainz with 15 goals last season, followed up to score from the rebound.

The home side equalised three minutes later with a little help from the visitors as Mainz midfielder Geis passed straight to Paderborn's Kachunga on the edge of the area.

The 22-year-old took a touch before hammering the ball low to the right of Mainz keeper Loris Karius.

Paderborn continued to press after the break but Mainz defender Niko Bungert flashed a header wide from a corner with 12 minutes remaining.

The home side did get in front though when Marvin Bakalorz picked out Hunemeier with a brilliant cross field pass. The Paderborn defender's header looped into the net despite Karius getting a hand to it.

Okazaki headed against the bar in the final minute of normal of time but there was to be another twist when Hunemeier barged into the Japanese forward inside the penalty area.

Paderborn 'keeper Lukas Kruse guessed correctly but Koo's spot kick still found the corner to salvage a point for Mainz.

"I think we played too nervously in the second half," Mainz's new Danish coach Kasper Hjulmand said.

"We showed good spirit in the last few minutes and that was very important for us."

On Saturday evening, Bayer Leverkusen's Karim Bellarabi hit the Bundesliga's fastest ever goal as title hopefuls Borussia Dortmund lost 2-0 in their opening game.

The Leverkusen attacker struck after just nine seconds and then set up Stefan Kiessling in injury time as the visitors won in Dortmund for the second season in a row.

Earlier Hoffenheim scored two goals in three first-half minutes to beat Augsburg 2-0 while Eintracht Frankfurst beat Freiburg 1-0.

On Friday, goals from Thomas Mueller and Arjen Robben helped defending champions Bayern Munich open with a 2-1 home win over VfL Wolfsburg.