Belfast Giants endured a second defeat by Cardiff in 24 hours after their slim Elite League title hopes had been ended by Sheffield's win over Coventry.
After Saturday's 5-2 defeat, Belfast took Cardiff to overtime on Sunday before the Devils clinched a 4-3 win.
Goals from Kris Beech and Mike Forney put Belfast 2-0 up on Sunday.
A Zach Hervato goal and two Jake Morissette strikes edged Cardiff 3-2 ahead before Chris Higgins levelled but Tomas Kurka hit an overtime winner.
Sheffield's earlier 6-3 victory over Coventry maintained their two-point advantage over Cardiff after the weekend.
That Steelers win ended any slim mathematical possibility of the Giants regaining the league title.
Belfast's only remaining chance of silverware this season now rests with the end-of-campaign play-offs.
The Giants will complete their league campaign in the coming week as Wednesday's home contest with Cardiff is followed by back-to-back games against Fife at the SSE Arena on Friday and Saturday.