In the battle of the Schmidts, Martin opted to make two changes to his side that played during midweek. Bell and Pablo de Blasis came in for Niko Bungert (not in squad) and Christian Clemens (bench).
As for Roger and Bayer Leverkusen, more alterations were in order. Ömer Toprak, Admir Mehmedi, Julian Brandt and Joel Pohjanpalo were restored to the starting eleven, with Jonathan Tah, Kevin Volland (bench), Hakan Calhanoglu and Lars Bender (not in squad) dropping out.
Flurry of goals sees Mainz go into the break ahead
It was an even opening to the game as both sides had their chances but failed to create that one clear-cut opportunity needed. Levin Öztunali and Gaetan Bussmann both went close for Mainz while Julian Brandt and Wendell provided the main threat for Leverkusen; the hosts were dealt a blow as Leon Balogun was forced off injured, though.
It was end-to-end without goals until the half hour, when Mainz struck first. A superb ball through to Öztunali from Daniel Brosinski set the former Leverkusen winger through on goal. He was soon joined by Malli, and Öztunali unselfishly squared for his Turkish team-mate to tap into an empty net.
That joy would prove to be short-lived however, as Charles Aranguiz managed to pick out Hernandez lurking behind the Mainz defence. After timing his run to perfection, the hot-shot forward controlled brilliantly before producing a finish of real quality to leave Jonas Lössl without a hope.
The drama didn't end there and Mainz struck once more - the third goal in five minutes - to retake the lead. A corner was swung into the six-yard box by Malli and missed by everyone, only to fall into the feet of Bell. He didn't know much about it but the centre-half certainly wasn't complaining as his side had the advantage at the break.
Hernandez turns it around for Leverkusen
The opening 15 minutes of the second half saw Leverkusen come out and try to get back on terms as quickly as possible. However, they were up against some really dogged and desperate Mainz defending, who were keen to not give up an inch to their opponents. That was evidenced by Hack, who seemed to be in the way of every shot and cross.
Eventually, though, the pressure told on the tiring Mainz back-line. Stefan Kießling, who had come on just two minutes prior, provided the crucial assist as he set-up Hernandez to double his tally. The Mexican thundered a shot at goal from 12 yards but a nasty deflection off Hack looped the ball up and over the helpless Lössl.
Mainz were struggling to hold onto the ball or move forward in the second half and were almost made to pay at the death. Volland's deflected cross was volleyed to the back post and Hernandez, but he couldn't grab his hat-trick with the simplest chance of the lot as he rattled the post from just two yards out.
Hands on head, the former Manchester United striker thought he had missed his chance to give his side the win but Mainz didn't learn their lesson. Tah lobbed the ball over the Mainz back-line and Hernandez beat Lössl to the ball to send the away section into rapture and secure a much-needed win for the visitors.