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Bradley Goldberg's first-half double means Welling are on course for a top-three finish in National League South.
Goldberg's brace means the Wings need just one more win from their last two games to finish in the top three.
But Steve King's men might even have eyes on second spot after Woking went down at home to Concord on Good Friday.
Welling got off to the best possible start, going ahead inside just 50 seconds.
Danny Mills won a flick-on to set up Goldberg and he burst forward to the edge of the box before firing low beyond keeoer Nathan McDonald.
The Wings dominated the first 25 minutes without ever creating too many openings. However, they almost gifted Chelmsford an equaliser when defender Richard Orlu attempted to clear Chris Whelpdale's long throw and keeper Dan Wilks needed to claw the ball away from his own net.
Mills continued to cause Chelmsford all sorts of problems, closing down defenders and winning every header.
It needed a smart save from McDonald to deny Goldberg after he got the better of Adrian Cascaval.
Chelmsford were reduced to 10 men on 36 minutes. The dangerous Mills played in Brendan Kiernan who was hauled down by Chez Isaac, who was rightly shown the red card by Matty Buonassisi.
Goldberg promptly tucked away the penalty to put Welling 2-0 ahead.
It was a testing half for referee Buonassisi as players and management from both sides appealed for every decision but he came through it with flying colours.
Chelmsford started the second half on top, with Rhys Murphy - fortunate not to be booked for diving in the first half - seeing an early effort cleared off the line by Craig Braham-Barrett.
It set the tone for the second half although Chelmsford lacked a cutting edge in the final third.
As an attacking force, Welling were virtually non-existent after the break but they knew that the game was already firmly in their control and had no reason to rush forward.
Goldberg was denied a hat-trick in stoppage time when McDonald tipped over his header from a Luke Rooney free-kick.
Welling: Wilks, Ming, Braham-Barrett, Mendy, Orlu, Audel, Kiernan, Ijaha (Acheampong 90mins), Mills (Bettamer 83mins), Goldberg, McCallum (Rooney 74mins). Subs not used: Newton, Genovesi.
Chelmsford: McDonald, Omozusi, Porter, Spillane, Giles (Chiedozie 55mins), Church, Isaac, Anderson, Cascaval (Reynolds 46mins), Whelpdale, Murphy (Cosgrave 70mins). Subs not used: Barnum-Bobb, Cosgrave, Young.
Attendance: 934.