Jurgen Klopp said his Borussia Dortmund side was drained after booking its place in the DFB Pokal final with a 2-0 win over Wolfsburg.
BVB beat Real Madrid 2-0 in the second leg of its Champions League quarterfinal seven days ago, before thrashing Bayern 3-0 on Saturday, prior to Tuesday's semifinal clash.
The exertions of the past seven days appeared to take their toll, with Wolfsburg creating several good opportunities during the 90 minutes, though BVB's superior quality eventually emerged.
Henrikh Mkhitaryan opened the scoring in the first half and Robert Lewandowski doubled Dortmund's lead with his 100th goal for the club before halftime, with Klopp relieved to see his players come through a stern test.
"We have made the final, all is well," he told reporters after the game. "With the quality that Wolfsburg have it is normal they have chance. The boys have played a lot of football and today it has taken its toll for the first time.
"Wolfsburg always stayed focused and we had our chances on the break, but we didn't have our usual control because of a lack of freshness."
Defender Mats Hummels was relieved after the game and said Wolfsburg was unfortunate not to have something to show for its efforts.
"Despite the 2-0 result, that was very close. We were lucky that Wolfsburg didn't score, they had really good chances. We're glad that we made it to the final."