The duo have started the last nine games in all competitions for the Royals, conceding only six goals and not allowing any opponents to score more than once in that sequence.
McDermott told the club's official website: "Matt is our skipper, he's growing as a person and as a captain day by day.
"Matt has played more games than Alex at this level, but Alex is getting his reward for everything he does, the way he lives his life, he's a credit to himself."
Mills also credited his defensive team-mate, saying: "I think we've got a good partnership going at the moment, it was good to build on that with a clean sheet against West Brom.
"We're a very honest bunch of lads who are prepared to put in the graft and reap the rewards."