Glentoran followed up Monday's win over Glenavon with a comfortable Premiership victory against the Sky Blues.
Jonathan Smith converted an early penalty at the Oval before the Glens forward dragged a good chance wide.
Ciaran Caldwell's crisp strike into the bottom corner doubled the lead against a sluggish United team.
Ballymena improved after the break but failed to created clear-cut chances and Smith almost added a third for the hosts when he hit the woodwork.
The hosts dominated the first half and were good value for their 2-0 advantage at the break.
United protested when a penalty was awarded for Jim Ervin's challenge on Smith but the young forward kept his composure to slot in a ninth-minute opener.
Caldwell rifled home on 21 minutes and the Glens could have added to their tally as Ballymena struggled.
The visitors gained a foothold in the second half but were restricted to long-range efforts.
Smith struck a post from close range and Curtis Allen headed over at the backpost as Glentoran finished strongly.
What they said
Glentoran manager Alan Kernaghan said: "We were shipping plenty of goals but the boys have been magnificent in turning things around.
"The players showed grit and determination in the game and we got another clean sheet - the only thing that has changed is the workrate and attitude."