Bayer Leverkusen coach Xabi Alonso said he had a "bitter" feeling after the German champions saw their impressive unbeaten run in the Bundesliga end with a 3-2 defeat by RB Leipzig on Saturday.

Under Alonso, Leverkusen have made crucial late goals a speciality. It briefly seemed like that might happen again when the referee went to review a possible penalty in the 86th minute after Leipzig's Castello Lukeba and Leverkusen's Patrik Schick made contact.

The referee decided against the spot kick and Leverkusen lost to a German opponent for the first time since May 2023 after 35 Bundesliga games unbeaten, including their entire title-winning 2023-24 season.

"It's hard, it's bitter," Alonso told German broadcaster Sky. "I don't think we deserved to lose today."

The defeat left Leverkusen one result away from matching Hamburg's tally of 36 games unbeaten in 1982-83 -- the Bundesliga's second-longest run after Bayern Munich's record of 53 under Pep Guardiola.

Leipzig came back from 2-0 down as they made the most of relatively few chances, generally on the counter, to seal a comeback win. Their three goals came from 10 shots to Leverkusen's 27.

Leverkusen scored twice in the space of six first-half minutes, first when Jeremie Frimpong intercepted a loose pass, sent defender El Chadaille Bitshiabu the wrong way and beat goalkeeper Péter Gulácsi. Alex Grimaldo then finished off a team move that included new signing Martin Terrier drawing Gulacsi out of position.

Still, the momentum was with Leipzig at half-time after Kevin Kampl's added-time header, and Openda then turned the game around with two precise finishes. He leveled the score with a shot from a tight angle near the touchline, and made it 3-2 with a curling effort from outside the box.

"We'll take a lot of positives and negatives from this game," Alonso told a press conference.

"We played a good game in the first half. We were happy with that and wanted to build on it in the second. [But] We had no control in the second half and gave Leipzig too much space. We didn't do well in the back line.

"We will learn from these mistakes. It's not good to let an opponent come back after leading 2-0. But it's a process, we're still early in the season."

Alonso called for more unity in defence as his team look to retain their title this season.

"We were in a good flow after taking a 2-0 lead, but we then have to be ready to defend," Alonso added.

"We want to attack together, but we also have to defend together. We'll work through the game after the international break."

Leverkusen were the better side and could have gained a bigger advantage before the break with early chances through Edmond Tapsoba and Piero Hincapié, the latter hitting the bar with a header.

"Of course it hurts because we didn't take our chances today," said Frimpong.

"In the end we lost because Leipzig took their chances better. It was a good game, but we have to score goals. We will continue to work on that in training."

Leverkusen next visit Hoffenheim on Sept. 14 before travelling to Feyenoord for their Champions League opener five days later.

Information from The Associated Press and Reuters contributed to this report.