Mainz had scored big upsets recently against Leverkusen and Bayern, so Dortmund weren't underestimating the visitors. For their part, Mainz looked as though someone had pricked their bubble, never threatening the home goal in the full 90 minutes.

On the half-hour mark, after a sleepy opening phase, Gonzalo Castro took an extended stroll through a seemingly mesmerized Mainz midfield, evading four markers and passing to Marco Reus. The 26-year-old finished easily for his ninth goal of the campaign.

A few ticks of the clock later, Mainz keeper Loris Karius just got his fingertips to a long pass to prevent Tuchel's men from doubling their lead.

After the break it was more of the same. Dortmund should have increased their lead in the 50th minute, but Pierre-Emerick Aubameyang contrived to blow a trio of sitters within 60 seconds.

It was much the same situation 15 minutes later, as Karius parried close-range shots by Reus and Henrikh Mkhitaryan. At that point in the match, Dortmund had created 15 shots to Mainz's three and were controlling the ball more than two-thirds of the time.

But the outcome of the match receded into insignificance, as it emerged that a fan had died of a heart attack in his seat, and another had to be taken to the hospital possibly with cardiac arrest. The normally raucous southern terraces fell uncharacteristically silent in shock.

Seemingly unaware of that tragic event, Dortmund continued to press, and Shinji Kagawa finally put the game on ice with a goal in the 72nd minute.

"We players didn't know what was going on, and we wondered why everyone had gone silent," Reus said after the match. "Afterwards the coaches told us what had happened."

The referee blew the final whistle on 90 minutes exactly. Dortmund had won 2-0, but out of respect for the deceased fan and his loved ones, there were no celebrations. The result on this sad afternoon means second-placed Dortmund stay five points behind Bayern. Mainz remain sixth.

Hamburg shoot selves in foot

Hamburg came into their away match against Leverkusen on the heels of what their coach described as their best performance of the season. The hosts, on the other hand, were winless in their last four league matches - a disappointing stretch for a would-be Champions League contender at a crucial point in the season.

Leverkusen coach Roger Schmidt was back on the touchline after serving a three-match suspension for referee disobedience, and Hamburg offered him and his charges an early gift to help them out of their rut. After 18 minutes, Albin Ekdal deflected a Julian Brandt shot past Rene Adler for an own goal. Leverkusen's lucky lead seemed to unsettle the visitors, who failed to manufacture a good look in the first half.

The hosts remained the better side after the interval, and goalkeeper Bernd Leno was on hand to diffuse the situation when Artjoms Rudnevs who had a go from 12 meters out (39 feet) shortly before the hour mark.

Hamburg threw everything but the kitchen sink forward, and 10 minutes from time, Leno pulled off another fine reflex save as Rudnevs took aim from further in. Tin Jedvaj saw two quick yellow cards as the clock ticked down. But the sending-off had no effect.

Ultimately, the visitors deserved an equalizer, but Leverkusen held on to secure a nervy 1-0 win. That took them up to seventh in the table. Hamburg are in no-man's land in 12th.