A double from Jake Cassidy helped end Dover’s unbeaten run after a goal fest at Crabble.
Dover took the early lead through Sotiriou, but were pegged back by Maidenhead, who took advantage of some lacklustre defending to take all three points.
Earlier in the day, Dover boss Andy Hessenthaler, who was managing Whites for the 200th time in the National League, made one change from the draw against Solihull Moors, with Ruel Sotiriou coming in for his first start, replacing Steve Rigg.
It was the Cypriot who got Whites off to the best start possible inside five minutes with a bullet header from a corner from Bobby-Joe Taylor.
Maidenhead hit back minutes later through Cassidy who drove his shot into the bottom corner, giving goalkeeper Yusuf Mersin no chance.
Shortly after, Sotiriou put the hosts back in front to double his tally for the game when his shot in the box beat the goalkeeper.
Remy Clerima then had a great chance to equalise for The Magpies when a corner from Josh Smile found the defender who looked to backheel it past the goalkeeper.
Dover would’ve gone two in front if Chris Dunn hadn’t produced a great save to deny Jai Reason who shot from just outside the area.
Maidenhead looked more dangerous as the half went on and would’ve equalised but forMichael Woods goal-line clearance.
The equaliser came shortly after through Ryan Upward who had a shot from the edge of the box which fired past Mersin into the bottom corner.
Shortly before half time the visitors took the lead for the first half through Cassidy with his second of the game, after a defensive mistake allowed the attacker through on goal who finished into the bottom corner.
Maidenhead doubled their lead shortly after the break after a great through ball found Joe Ellul who poked the ball past Mersin.
Paul Rooney got Whites back in it midway through the second half after a free kick by Bobby-Joe Taylor found the head of the centre half who nodded home to give Whites a lifeline.
Sotiriou then had a massive chance to get Dover level as well as getting his hat trick. Ricky Modeste went down in the box under the challenge of Ellul, however Dunn made a great save to deny the Cypriot’s spot-kick.
Late on Ellul got sent off for a second bookable offence, but it was too late for Dover to really take advantage of the extra man.
Dover will be back in FA Cup action on Sunday as they travel to League One promotion challengers Peterborough in the Second Round.
Dover Athletic: Mersin, Simpson, Doe, Rooney, Taylor, Munns(L’Ghoul 58”), Woods, Gobern(Jeffrey 58”), Reason, Sotiriou, Effiong(Modeste 58”)
Subs not used: Roberto Ratti, De Havilland
Maidenhead United: Dunn, Clerima, Steer, Ellul, Davies(Grant 80”), Cassidy, Kelly, Sheckleford, Akintunde(Sekajja 75”), Upward, Smile
Subs not used: Mensah, Twumasi, Sekajja
Attendance: 687
Man of the match: Ruel Sotiriou
Referee: Lloyd Wood