The Belgium midfielder side-footed a Giovanni Reyna freekick past Mainz goalkeeper Robin Zentner with three minutes left to claim his first Bundesliga goal in two years.

“It was a hard game, sometimes you can’t play beautiful football and have to win like this,” Witsel told broadcaster DAZN.

“This was about body language and fighting spirit – for the second straight game we didn’t concede a goal,” he added, referring to Saturday’s 1-0 home win against Arminia Bielefeld.

“I am not a goal scorer, but I was very happy to get this one.”

The result saw second-placed Dortmund further reduce Bayern’s lead – which was 10 points on Saturday night – with the Bundesliga’s top two teams still to meet on April 23.

The original fixture was postponed 10 days ago due to an outbreak of Covid in the Mainz squad.

Dortmund struggled to break down the home defence before Witsel struck.

Zentner had repeatedly denied Dortmund’s attack, including star striker Erling Haaland, who came on for the last half-hour.

After Witsel finally broke the deadlock, Dortmund twice came within a whisker of doubling their lead in stoppage-time.

Julian Brandt fired just wide with the goal at his mercy before Reyna forced Zentner into a diving save from his freekick.