Klaas-Jan Huntelaar scored a hat-trick as Schalke cruised to their fifth straight home victory on Saturday, over a lacklustre Mainz side.
Di Matteo's men got off to the perfect start when Huntelaar latched onto a knock down by Choupo-Moting, and the Dutchman finished with aplomb, lobbing the ball over the goalkeeper under pressure from the defence.
Koo then missed two opportunities for the visitors, when he certainly should have done better, before Karius had to be alert to stop Huntelaar doubling his tally before the 20 minute mark.
He did just that after 25 minutes though, Max Meyer found himself deep in the penalty area, and his scuffed cross found Huntelaar, who couldn't miss from six yards out - notching up his 100th goal in Schalke colours.
The game was running away from the visitors, and Maxim Choupo-Moting could've sealed the points in the first half but for a fine save from Karius.
Diaz could've halved the deficit just after the half hour, but failed to hit the target with his effort, before Stefan Bell failed to beat Fahrmann from well inside the penalty area. Mainz were back in it just before the break though, a swinging ball found its way deep into the Schalke box, and a low shot squirmed under the body of Fahrmann leaving Okazaki the simple task of helping the ball over the line from a metre out.
Barnetta came on in the second half, giving the visitors another problem to deal with, and a problem he was - taking just eight minutes to make an impact, with a stunning strike. Huntelaar this time the creator, finding Barnetta 25 yards out, and the Swiss international curled a beautiful effort out of the reach of Karius to extend the lead to two.
That goal hit the visitors hard, and the fourth was not far away. Choupo-Moting threaded a ball through a tiny gap in the Mainz defence, and Huntelaar found himself one-on-one with the 'keeper, slotting the ball home easily to grab his hat-trick goal, and all three points for his side.
The home side sat back and allowed Mainz to attack after that, Geis and Koo both had efforts on goal, the latter going closest when he brought Fahrmann into action ten minutes from time.
It was the perfect response from di Matteo's men after their drubbing in midweek, and it was a win that puts huge pressure on two of the sides above them, Mönchengladbach and Wolfsburg, when they meet tomorrow.
The loss for Mainz extends their winless run to five games now, and although they sit ninth in the table, they hold just a four point lead over those sides in the bottom three.
Schalke travel to Stuttgart next week, while Mainz are again on their travels as the face Hamburg on Sunday.
