Alex Ferguson reveals Manchester United's striking ambition
Afterwards, Ferguson refused to blame the under-pressure de Gea for Southampton's goal, saying: "Michael's pass-back was a bit soft. Michael held his hand up -- it's great to see that, honest players like Michael saying 'Sorry boss, sorry lads'. It's great.
Manchester United manager Alex Ferguson has challenged his three main strikers to each reach 20 goals this season as the Old Trafford club aim for a trophy treble.
United moved seven points clear at the top of the Premier League table with a 2-1 win at home to Southampton on Wednesday.
They have an FA Cup fifth round tie to come against Reading and also face Real Madrid in the Champions League last 16 next month.
Rooney scored twice against the Saints to take his tally for the season to 12 goals, while Robin van Persie has scored 22 in all competitions and Javier Hernandez has managed 14.
Ferguson believes that if Rooney and Hernandez can join van Persie in passing the 20-goal mark it will have a key impact on United's chances of silverware.
"Wayne scored (in the 4-1 win over Fulham) on Saturday too and if Chicharito, Wayne and Robin give us over 20 goals each we're in business," Ferguson said.
"If you look at it my experience of this club and going for championships, there's always a game where you say we were a bit lucky and (the win against Southampton) was one of these nights.
"Winning is the name of the game at this stage of the season."
Southampton striker Jay Rodriguez opened the scoring after just two minutes at Old Trafford when United goalkeeper David de Gea failed to reach England midfielder Michael Carrick's back-pass.
But Rooney struck twice, driving in from a Shinji Kagawa pass and finishing from Patrice Evra's header, with his ninth goal in nine games securing victory for United.
Afterwards, Ferguson refused to blame the under-pressure de Gea for Southampton's goal, saying: "Michael's pass-back was a bit soft. Michael held his hand up -- it's great to see that, honest players like Michael saying 'Sorry boss, sorry lads'. It's great."
Southampton's new manager Mauricio Pochettino had sympathy for de Gea.
The Argentinian has spent the bulk of his managerial career so far in Spain with Espanyol and believes goalkeepers face a much tougher time in England than they do in La Liga.
"What's clear to me is that footballers do make mistakes and the first goal was a combination of mistakes and Jay being in the right place at the right time and being an opportunist," said Pochettino.
"It's clear to me that in any free-kick near the box and corners it presents a chance and a goalscoring opportunity and that doesn't happen as much in the Spanish league and the goalkeeper in Spain is more protected than here and that makes their job a lot harder."
Following the goalless draw with Everton in his opening match in charge of the south coast side, Pochettino took Southampton's players for a training break in Barcelona last week.
But despite utilising the Spanish giants' training facilities, Pochettino insisted he did not take any advice from Barcelona's coaching staff.
"The Barcelona pressing that used to be in the time of (former manager Pep) Guardiola isn't happening anymore.
"And Barcelona have a player in (Lionel) Messi that can score 100 goals a year, so what advice am I going to get?"
Next up for Pochettino is a match away to Saints' fellow strugglers Wigan on Saturday and the manager sees the game at the DW Stadium as a good opportunity to pull further away from trouble.
"All games have their complexity and difficulty but in any game where you have a chance of three points you have to go for the win."