The visitors came from one down as Jeremie Frimpong’s early strike was cancelled out by goals from Julian Brandt, Julian Ryerson, Karim Adeyemi and Serhou Guirassy.
Alonso, who took Leverkusen to a league and cup double last year in his first full season in charge, announced his impending departure from the club on Friday, with Real Madrid the Spaniard’s likely destination.
Alonso told reporters his exit was “emotional and this club will stay in my heart forever”, adding he would “forget the result from today pretty quickly”.
Leverkusen’s title defence fizzled out with a 2-2 draw at Freiburg last Sunday, but the home fans were in a celebratory mood, 12 months after Alonso took them to a first league title in their 120-year history.
Leverkusen centre-back Jonathan Tah, who is also leaving at season’s end, was full of praise for Alonso.
“He’s got a certain aura, he’s a great coach and a great person. We can be thankful to him,” said Tah.
Before the game, Leverkusen celebrated Alonso’s time at the club as fans chanted ‘Danke Xabi’ and held up placards with pictures of the Basque coach, but Dortmund were in no mood to celebrate.
The hosts dominated the opening period, pinning Dortmund in their own half. Only some spectacular saves from Dortmund goalkeeper Gregor Kobel, who made seven stops before half-time alone, kept Leverkusen at bay.
Leverkusen’s pressure finally told with 31 minutes gone when Florian Wirtz waltzed through the penalty area, attracted three defenders before laying the ball off to Frimpong who curled a shot into the top corner.
Dortmund had barely left their own half but the goal shook them to life. The visitors equalised two minutes later, Adeyemi cutting the ball back for Brandt to hammer home.
Brandt engineered Dortmund’s second two minutes before the break, winning a ball near the sideline and finding a cross to Pascal Gross, who swivelled and teed up Ryerson to drive a low shot into the net.
Both Adeyemi and Guirassy, who each scored braces in last week’s 4-0 thumping of Wolfsburg, got on the scoresheet in the space of four second-half minutes.
Guirassy now has 33 goals from 44 games in his first season in Dortmund. Wirtz, who has been linked with a summer departure, laid on a late consolation goal for Jonas Hofmann in stoppage time.
Alonso will coach Leverkusen one more time, in next week’s game at Mainz, but Leverkusen cannot finish any higher or lower than second.
At one point sitting 12th, Dortmund have picked up 19 of a possible 21 points and now sit one point behind fourth-placed Freiburg.
“It’s not in our hands but we’re a bit closer and we’ve got one more final next week at home,” coach Niko Kovac told DAZN.
Dortmund’s job was made a little easier when third-placed Eintracht Frankfurt were held to a 2-2 draw at home to St Pauli later on Sunday.
Rasmus Kristensen opened the scoring with a stunner after just 23 seconds but St Pauli quickly turned the match around as goals from Manolis Saliakas and Morgan Guilavogui fired the visitors ahead.
Former Chelsea striker Michy Batshuayi equalised on 71 minutes and had the ball in the net again in the dying stages, but the goal was chalked off for handball.
Frankfurt stay third but face fourth-placed Freiburg next week, with the winners guaranteed to play in the Champions League. Dortmund need to beat relegated Holstein Kiel at home to join them.
In Sunday’s final match, Stuttgart dominated 10-man Augsburg at home in a 4-0 win, with goals from Atakan Karazor, Nick Woltemade, Enzo Millot and Ermedin Demirovic.
Stuttgart will face third-division Arminia Bielefeld in the German Cup final on May 24. (AFP)
