Both teams started 2014 with last-gasp victories after Dons midfielder Peter Pawlett struck in stoppage time on New Year's Day against Dundee United, while Kris Boyd's sixth goal in six games killed off St Mirren 24 hours later.
The Rugby Park outfit's 2-1 win over Danny Lennon's side mean they end the festive period having collected nine points from a possible 12.
They now sit eighth in the Scottish Premiership but are still 17 points behind the third-placed Pittodrie side, who visit Ayrshire next.
Johnston reckons the side bossed by Derek McInnes will not drop any lower than their current slot by the time the Europa League places are decided in May.
But he has backed his players to take another big scalp after recovering from their slow start to the campaign.
The Killie manager said: "I was at Aberdeen's game against Dundee United the other day and they are a top team. You have seen that from the start of the season.
'They are going to be up there in second or third with the quality of squad they have got.
"We know how much of a challenge it will be and we'll have to be at our very best. But we can take a lot of credit for our performance against St Mirren and we will welcome them here believing we can beat them."