Lining up alongside fellow arrival Sandro Tonali and Conor Gallagher in midfield, our summer capture from West Ham made his mark in superb style on his first appearance in Lilywhite.
Mathys Tel swung in a corner, goalkeeper Craig MacGillivray punched high and clear only for Mateus to thunder back a volley that pinged home off the inside of the post. It was a goal worthy of winning any game - in this case, it was enough to beat a well-organised, competitive MK side.
There was a welcome return to action for Ben Davies - out since January - with Kota Takai and Manor Solomon also back in Lilywhite after loan spells last season as we took on the League One side in our pre-season opener - exactly a month away from the big kick-off in the Premier League at Brentford.
As expected, we controlled possession and territory although clear-cut chances were at a premium against MK's 5-4-1 system. MacGillivray had already denied Dominic Solanke from close range before Fernandes' wonder strike and he was there again to save with his feet from Solomon after a one-two with Gallagher.
As we probed away, using Tel and Solomon wide, Archie Gray looking to push on from right-back, a couple of deliveries fizzed across goal but the closest we came was when Tonali threaded through to Tel and Gallagher was inches away from the cross.
Martin Dubravka joined Fernandes and Tonali in making their first appearances as Robert De Zerbi switched 11 players for the second half.
Richarlison was unlucky to see a clever finish ruled out by an offside flag, Mikey Moore's goalbound strike was blocked and at the other end, Craig Patterson's drive from the angle was straight at Dubravka.
Our final chances of note arrived in quick succession as Richarlison went for power one-on-one against MacGillivray, who parried away and Yang Min-Hyeok looked to have done it all right when he took in Luca Williams-Barnett's pass only to miss the target. MK had the last opportunity as Dubravka reacted brilliantly to tip over Ben Wiles header from 10 yards.
The players will now fly out to Auckland, New Zealand for the the first part of our pre-season tour, taking on Auckland at Eden Park in the early hours of Sunday morning (4am UK).
Line-ups
Spurs: First half: Kinsky, Gray, Takai, Davies, Kyerematen, Tonali, Fernandes, Gallagher, Solomon, Tel, Solanke.
Second half: Dubravka, Tye Hall, Hardy, Byrne, Kyerematen, Donley, Williams-Barnett, Moore, Yang, Scarlett, Richarlison.
Starting XI: MacGillivray (Stacey 80), Barlaser (Matete 46), Bramall (Kazungu 66), Crowley (Lewis-Burgess 56; Silver 80), Goode (Perniskie 66), Hepburn-Murphy (Boateng 66), Jones (Wiles 56), Paterson (Ekpiteta 66), Sanders (Burke 66), Waller (Nelson 46), Wintle (Kelly 46).
Match data
Goal: Spurs - Fernandes 4.
Referee: Constantine Hatzidakis.
Venue: Hotspur Way, Enfield.
Weather: Cloudy, warm, 26 degrees at kick-off.