Manager Gordon Strachan has refused to throw in the towel despite the odds being against a late challenge.
In his match programme notes, Strachan said: "I certainly have not given up hope of a play-off place, because any team that can put five wins together will get one of those spots.
"The games are running out, of course, and after tonight we have just three home League games at the Riverside. This is certainly not the time to slacken off.
"While there is a possibility of a play-off place, I will be demanding maximum energy and commitment from all my players. I expect nothing less of professionals and I know the fans are also hoping that we can end the season on a high."
A virus ruled out Middlesbrough skipper Gary O'Neil, midfield player Julio Arca and centre-forward Scott McDonald.
Preston defender Sean St Ledger was back at the Riverside Stadium after his loan spell at Middlesbrough earlier in the season.
Preston were the first to threaten and only a brilliant Brad Jones save prevented Ross Wallace scoring with a powerful 25-yard free-kick.
The visitors were more lively in attack in the early stages of the game with Chris Brown prominent and Jones had to get down well to save from Darren Carter at the near post.
On balance, Preston deserved to be ahead but in the 29th minute Middlesbrough took the lead. From Barry Robson's free-kick, Chris Killen headed into the far corner to score his second goal in successive matches.
Jones was by far the busier goalkeeper in the first half. After being the target of Boro's boo-boys early in the season, the Australian shot-stopper in now back in favour.
Preston pressed strongly in search of an equaliser but met stubborn resistance from Middlesbrough's defence although the visitors were desperately unlucky not to score when a fierce Wallace shot struck a post.
The referee turned down strong Preston penalty appeals much to the fury of manager Darren Ferguson on the touchline and the 560 visiting fans behind the goal.
Middlesbrough wrapped up the points when 19-year-old Jonathan Franks scored his first home goal in the 90th minute but Preston could consider themselves unlucky not to gain a point from the game.