Sir Alex Ferguson has warned his Manchester United stars they cannot be as wasteful against Benfica as they were at Middlesbrough if they are to keep their Champions League dreams alive.
United welcome the Portuguese side to Old Trafford on Wednesday evening needing a draw to secure their passage to the knockout stage.
The Reds are six points clear at the top of the Premiership and will increase their lead over champions Chelsea, for 24 hours at least, if they win the Manchester derby on Saturday.
But Ferguson admits they will need to be more ruthless in front of goal if they are to mount a sustained charged for the title.
At the Riverside Stadium on Saturday they were indebted not only to the unsteady feet of Cristiano Ronaldo, but the endeavour of midfielder Darren Fletcher, whose 68th-minute header clinched victory long after it should have been secured.
Ferguson told MUTV: 'With the chances we had we should have had the game sewn up long before. We should have had five or six goals.
'It (missing chances) has happened a few times away from home this season. Although our form has been consistently good, you cannot flirt with all these missed chances all the time.
'Sometimes you are going to suffer. We got a warning today when they equalised with 20 minutes to go.
'As long as we remember to finish teams off, we will be okay. This (Benfica) is a game you cannot trifle with.
'It is too important for us. If you get chances take them - and I think we have got a chance.'
Louis Saha had already seen a header blocked on the line by Robert Huth when he gave his side the lead, although his strike proved a talking point for more than one reason.
The Frenchman injected pace and craft into a flowing move with a delicious turn before racing past Jonathan Woodgate - who had been unwell before the game and failed to re-appear after the break - and then fed Ronaldo as he cut into the box from the right.
Boro goalkeeper Mark Schwarzer was swift to spot the danger but not quick enough to get there before the Portuguese international, who skipped past the Australian before collapsing in a heap, prompting referee Chris Foy to point to the spot.
Schwarzer and his team-mates were furious and television replays showed there had been no contact.
Southgate later delivered a withering verdict on the winger's contribution, but Ferguson said: 'It does look as though the goalkeeper did not touch him. But it is intent (from Schwarzer).
'What could he (Ronaldo) do? He was going to be carted anyway. I think it is a penalty.'
Saha, who had seen his last spot-kick saved as Celtic clinched a famous Champions League victory, stepped up to beat the keeper with a firm strike to put the visitors ahead.
Ferguson had left the decision over who took any penalties to Saha and Ronaldo, and Wayne Rooney praised his team-mate for his courage.
He said: 'Louis is the penalty taker. Everyone misses penalties, it's part of football. Louis was brave enough to step up and take a penalty.'
United were in control until Woodgate's departure, which saw Southgate introduce James Morrison and change his system from 3-5-2 to 4-4-2.
The newcomer made an impact with 66 minutes gone when he volleyed the equaliser sweetly past Edwin van der Sar after Gabriel Heinze could only help on Stewart Downing's cross.
However, Boro's joy was shortlived and just two minutes later, Ronaldo set up Ryan Giggs to cross for Fletcher who powered the winner past a helpless Schwarzer.
Southgate said: 'We scored after a good spell for us and got back into the game, and then we switched off at a time when we needed to be disciplined.
'We did not do the right things and that ultimately cost us a point.
'We were never out of the game. Right to the last minute, we had a chance to equalise.
'I cannot ask any more in terms of character, commitment and attitude - it was excellent again.
'But a little more quality at times was required and we switched off 30 seconds after the goal, and that is a lesson learned.'