Bolton manager Gary Megson believes victory at Portsmouth on Saturday will all but guarantee his side's Premier League survival.Wanderers are 12th with 37 points and a seven-point cushion over the relegation zone, but have only won once in their last five league games and have conceded nine goals in that time.Four of those came last weekend at Chelsea, but Megson was able to take plenty of positives from the defeat, during which Bolton made a stirring second-half comeback from 4-0 down to almost snatch a draw.Megson will be hoping for more of the same on Saturday at relegation-threatened Portsmouth to reach the all-important 40-point mark, although he describes setting points targets as a dangerous game.Asked if one more win will secure Bolton's top-flight status, Megson said: "Mathematically no, but it will be a huge boost for us to get to 40 points."It will be massive fillip for us if we can get that win down at Portsmouth and come back to the Reebok in that position."Nobody knows what it will take to stay up so we've just got to keep plugging away."All the people who said it will be 42 points to stay up might feel a little bit different now. One even said a while back it would take 37 points. We just want to get as many points as we can. I think it's a dangerous thing to set yourself a finish line before the end of the season."Megson is expecting a vociferous reception at Fratton Park against a side managed by his old friend Paul Hart, a former team-mate at Sheffield Wednesday.Pompey scraped a 2-2 draw last weekend against rock-bottom West Brom but they are unbeaten in four and Megson is wary of the threat they pose to his team."Paul's got the biggest side in the league in terms of stature and height so set pieces might be a problem so we need to be ready for that," he said."The fans down there would have been looking at these two fixtures - us and West Brom last week - to take six points. They got one point last week and now the expectation is to get three points at home against us. It's a massive game for them because they are at home. And it's a huge game for us too because it's another step towards safety."I knew Paul when we were both at Sheffield Wednesday. I always thought he would go into management - he always wanted to."The job he's done at Portsmouth has been excellent. He would have been given a brief to steady the ship a bit, which he has done, and keep them in the Premier League."I'm sure they'll come out all guns blazing because they know it's an opportunity for them to get three points at home and we've got to stand up and make sure we battle for every blade of grass."Midfielder Chris Basham could feature after his impressive performance as a substitute at Stamford Bridge. The 20-year-old afterwards revealed he is hoping for a new contract with the Trotters, but Megson urged him to be patient."Chris Basham can't be concentrating on his contract and he won't be because he's not that type of lad, but it will get sorted out," he added."He just needs to concentrate on his football and his development and everything else will take care of itself."