St Johnstone manager Tommy Wright is starting to eye a challenge for second spot in the Ladbrokes Premiership - but he knows their winning run can be fragile if they do not remain focused.

St Johnstone were 16 points behind Aberdeen after eight games, but will leapfrog the Dons into third place if they beat Tayside rivals Dundee at McDiarmid Park on Friday night.

Saints are looking for a sixth consecutive victory but Wright is equally aware that teams can suffer a downturn in form in Scotland's top flight and wants to guard against it.

"Confidence is high but we never get carried away," Wright said. "We know this game can change very quickly.

"What we have done, and it's less than halfway to the split, is give ourselves a good position to get top six and put pressure on Aberdeen and Hearts. Nobody is saying we are going to finish second but we have put ourselves in a good position to challenge.

"To do that we have to maintain the performances and results we have been getting because they are two very good sides and they will win more than they lose.

"Victory would put us eight points ahead of Dundee which is good at this stage but we keep reminding ourselves that last year Dundee United were 16 or 18 points ahead of us and we managed to pip them.

"We could get into third place with a win, maybe for only 24 hours, but we could do it. That's an incentive and also it's a derby and derby games are a wee bit special."

Aberdeen quickly went from winning their first eight games to losing 5-1 at home to Saints.

"That's how it can change so quickly, Aberdeen haven't done a lot wrong and then they lose and that can happen so quickly in this league," Wright said.

"That's why we have to stay focused. We know if we keep doing what we are doing that we can challenge for second but we also know if we get into a bad run you can quite easily slip out of it, and it can happen so quickly."

The Perth side look to have real strength in depth this season and Wright is trying to sign more players up on extended contracts following skipper Dave Mackay's new deal, in an attempt to continue the club's recent stability.

"We don't look to have to bring in seven or eight in the summer," he said.

"I know that doesn't excite the fans sometimes but we plan. We are already talking to one or two who are coming out of contract and we are a wee bit down the road with those."