Russell Slade insists his team of underdogs must maximise everything they have to pull off a “truly remarkable” feat and win the League 1 play-offs.

Orient’s hopes of reaching the final at Wembley rest on their two-legged semi-final against sixth-placed Peterborough United. The O’s travel to London Road on Saturday (12.15pm kick-off) before the return match at Brisbane Road on Tuesday night.

Despite finishing the season in third, Slade believes his side are the outsiders for promotion. He insists Orient will have to show all the qualities which saw them challenge for automatic promotion for much of the campaign, if they are to win a place in the Championship.

Slade said: “We’ve got a mini league now and there’s an awful lot more football from our point of view to play for. We’ve come such a long way and we have to give absolutely everything if we’re going to achieve something that would be truly remarkable.”

He added: “We don’t have to change anything. We just have to maintain what we’ve done all season and it is a one off situation. It’s a now situation and there’s nothing for second place unfortunately. All those values, assets and strengths we’ve shown over a long hard season we have to show. We have to maximise everything we’ve got.

“That’s the sort of standard we set ourselves because we’re underdogs going into the play-offs. There is no doubt about that because you’ve only got to look at the bookies and we’re not given a chance.”

Orient will have to do something no side has done before and beat Peterborough in the play-offs. The Posh have won all three occasions when they have reached the knockout competition. with the last coming in 2011 when they defeated Huddersfield Town in the League 1 final.

Slade said: “They have an excellent play-off record and are an excellent side. Darren Ferguson’s done a great job and they’ve already won one competition [Johnstone’s Paint Trophy] this season and played at Wembley so they’ll be looking to get there again that’s for sure. We know it’s going to be very, very tough.”

The O’s boss has guided Grimsby Town and Yeovil Town to the play-offs during his managerial career but both times his side were beaten in the final.

Slade believes there is no advantage in having the second leg at home and also thinks previous results are irrelevant despite his side producing arguably their performance of the season when winning 3-1 at Peterborough in November. In the most recent meeting between the sides, United won 2-1 at the Matchroom Stadium in February after Orient conceded two late goals.

Slade said: “You learn a lot of things which obviously I will try to use going into the play-off situation we have on Saturday. But I’m not going to start talking about what those things are and give somebody else an advantage.

“We could have ended up playing against any of the three clubs, so it is what it is. People say it’s an advantage playing at home in the second leg but I’ve done it both ways and won the semi-finals both ways so I don’t think there is any advantage. It’s all about the current situation and on the day how you perform.”

Reflecting on past results, Slade said: “It counts for nothing trust me [victory at Peterborough]. At Grimsby I beat Cheltenham twice in the league and we got beaten by them in the play-off final. It counts for nothing. You’re barking up the wrong tree if that’s what you believe or think.”

Scott Cuthbert missed the 3-1 win at MK Dons on Saturday through injury but the Scottish defender is expected to be fit this weekend which could give Slade a fully fit squad to choose from.

The manager said: “He had a slight hip problem so we weren’t taking any chances which we haven’t done, as you well know, over the last few weeks. We weren’t going to risk him but we are pretty hopeful he will be available for Saturday.

“I was hoping for bingo on Friday and didn’t quite get it. I nearly said ‘house’ but didn’t quite get it because Scott pulled out on Thursday. I was hoping we would have a full house. That was the aim and head of sports science Lee Southernwood, and all my staff, have done a fantastic job throughout the 46 games. We will continue to do our very best to achieve what we’re all after.”

Orient finished the campaign with a record points total of 86 and closed with back-to-back victories to give them momentum heading into the semi-final.

Slade said: “Even before these two wins I actually thought we were playing some really good football without perhaps getting that bit of fortune or rub of the green. For example against Wolves and I didn’t think we deserved to lose at Crawley. It wasn’t a great performance but I certainly didn’t think we deserved to lose.

“There were some good performances without us getting the reward but the last two games we’ve got that reward and it’s nice to go into the play-offs having won two games.”