The US Open Championship winner from Northern Ireland - looking to close the gap on Race to Dubai leader Martin Kaymer this week - birdied the fourth to move to eight under par.
That was enough to put him one shot clear of the chasing pack as overnight leader John Parry dropped a shot at the second to fall back to seven under.
Joining Parry in second place were compatriots Danny Willett and Chris Gane as well as Spaniards José Manuel Lara and Javi Colomo.
Challenge Tour player Colomo looked set to establish the clubhouse target - he was six under for the day and had only three holes remaining with his fellow challengers all still on the front nine.
All three of the final group found trouble at the par three fifth, but while Lara got up-and-down for par and McDowell salvaged a bogey with a smart chip from the edge of the green, Parry took three shots to find the green then two putted.
Meanwhile Colomo holed a putt from the fringe at the 16th - his fourth birdie in a row - to move into the outright lead on eight under.
While McDowell was busy cementing second place on The Race to Dubai and looking to maintain form ahead of The Ryder Cup next month, Colomo, Lara and Parry were fighting for their European Tour futures.
Colomo needs a win to automatically get a card for 2011, while Lara is 130th and Parry 117th on The Race to Dubai – with only the top 115 earning playing privileges for next season.
Colomo was not alone in front for long – Willett finding the green in two at the par five sixth and leaving himself a tap in birdie.
Willett reached the green in two once again at the par five seventh and this time holed for eagle to reach ten under, but Colomo found trouble at the 17th and double bogeyed.
Gane holed birdie putts at the ninth tenth and 11th to join his fellow Englishman at the top of the leaderboard and their compatriot David Lynn chipped in at the tenth to join McDowell on nine under.