Manchester City manager Roberto Mancini believes defending the Premier League trophy will be harder than clinching the club's first title in 44 years.
City ended their long wait to be crowned kings of English football in the dying seconds of last season with two goals in stoppage-time to beat QPR 3-2 and pip bitter rivals Manchester United on goal difference.
But now United have key defender Nemanja Vidic back to fitness after missing half of last season and have also beaten City in the race to sign Dutch striker Robin van Persie from Arsenal.
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Van Persie was a long-time target for Mancini only for United boss Sir Alex Ferguson to clinch the £24 million deal this week.
With Chelsea also splashing the cash in a bid to close the gap on City, Mancini, whose side begin their title defence against promoted Southampton at Eastlands on Sunday, is under no illusions about the size of the task facing his team.
"It will be even harder than last year. United have played for the title every year for 20 years. Just because we won the championship last time, we can't change that," he said.
"Van Persie is one of the best strikers in the world - he is a really top player, the best striker last year. With Wayne Rooney, they will be the best strikers in the Premier League.
"They signed him because they needed another striker. They are better with Van Persie. We have four strikers, it was impossible for me to have another one.
"When you are champions everyone wants to beat you, starting with Southampton. For this reason it will be a difficult game.
"But I enjoy it, because to compete with Manchester United, with Arsenal, with Chelsea, is fantastic. To win the championship last year I think was an incredible achievement for us."
Mancini has so far signed one player since the end of last season, paying £12 million for Everton midfielder Jack Rodwell, who was on the substitutes' bench for England's 2-1 friendly win over Italy in midweek.
Rodwell, once a target for United amongst others, struggled to fulfill his potential at Everton, but the 22-year-old is relishing the chance to compete for major honours with City.
"It's a great opportunity, I'm still young and I'll be with great players I can learn from, so it's the perfect chance for me," he said.
"It's going to be a challenge, but that's why I came. I'm here to challenge myself mentally and technically, to push myself and improve. I believe in my ability.
"There are amazing players here, I know a few from the England set-up. There's a great manager and a great squad. Training with them every day will certainly improve me."
After the frustration of missing out on van Persie, Mancini would like to sign another senior player and continues to be linked with Roma midfielder Daniele de Rossi.
He said: "It's important to start with one (signing). Now we have a game and we have 10 days to the end of the transfer market."
City face Southampton without England full-back Micah Richards, who injured an ankle while on Olympic duty.
Mancini expects him to be out for at least three weeks, while England goalkeeper Joe Hart is also a likely absentee.
Hart will have a late fitness test on a back injury but Romanian Costel Pantilimon stands by to continue after playing in the 3-2 Community Shield victory over Chelsea last weekend.
England midfielder Gareth Barry, recovering from an abdominal injury, also misses the opener.
"He will need one or two games in the reserves to regain fitness," Mancini added.
