United lost 4-3 to St Mirren on Saturday and are without a home win in 10 SPL matches, yet victory at Aberdeen on Wednesday in the final match before the winter break could turn the momentum in favour of Peter Houston's side, who have in recent campaigns made late-season charges up the table.
"Aberdeen got a good victory against Dundee, but we've got to go there and hopefully take something out of the game," Rankin said.
"We need to start picking up points and start picking up wins. It's about momentum in this league and we need to get the momentum going quickly.
"We're sitting eighth, but the way we're looking at it we're nine points off second.
"We know if we put a run together, which we can, which we have done in the past, we're confident enough to say we can get to second place and push for a European place again.
"We just need to put a run together, get a few wins and push ourselves up the table."
United's defending was poor against the Buddies and has been for much of the campaign. The straight red card shown to defender Brian McLean means United will be forced into a defensive reshuffle at Pittodrie. Unless Sean Dillon recovers sooner than expected from a thigh injury, captain Jon Daly is likely to drop back from striker to centre-back. Rankin was at a loss to explain the defensive woes of his side.
"We're scoring goals and creating a lot of chances, it's just at the back individual errors are costing us," Rankin added.
"Sooner or later hopefully our luck will change. It's disappointing the way its going just now."
Rankin's fellow midfielder Willo Flood went off midway through the first half with a groin problem and is also a doubt for the Dons match, which comes before the two-week hiatus.