LONDON (AFP) - Only six Premier League sides were left in the last 16 of this season's FA Cup after Sheffield United beat Manchester City 2-1 at Bramall Lane on Sunday.

The Blades, relegated to the second-tier Championship at the end of last season, were 2-0 up inside 25 minutes through Luton Shelton's balloon-assisted opener and Jonathan Stead before City substitute Daniel Sturridge pulled one back early in the second half.

City's defeat left Arsenal, holders Chelsea, Liverpool, Middlesbrough, Portsmouth and Manchester United - who beat Tottenham 3-1 earlier on Sunday - as the lone representatives from English football's top flight left in the hat for Monday's fifth round draw.

"The first-half went wrong," said City manager Sven-Goran Eriksson.

"We were not up for it and we lost too many balls up front and in midfield. We got better in the second half but it was not enough.

"It's the beauty of the Cup which hit us today. You can't just play good football, you have to battle as well."

City went behind in bizarre fashion with a goal that owed much to the balloons in their colours littering the pitch in front of Joe Hart's goal.

Lee Martin, on loan from Manchester United, delivered a low cross that took a slight deflection off the leg of City captain Richard Dunne.

The ball also clipped a balloon, a deviation that appeared to deceive Michael Ball as he missed his clearance.

It almost confused Shelton too but the Jamaica international kept his composure and beat Hart from six yards in the 12th minute.

A bemused Eriksson said: "It's a very strange goal. The ball changed direction, two balloons made a one-two with Michael Ball.

"We asked the fourth official twice during the first-half to ask the referee to stop the game and clear the pitch.

"The referee told Joe Hart to clear it when the ball was in the other half of the pitch but that's not right - you can't ask a player when the ball is live to clear the pitch.

"But it would be stupid of us to say we lost because of the balloons."

Blades manager Bryan Robson added: "It was a good win for us and our attacking play was very good.

"There was a bit of fortune about the first goal but we haven't been getting much luck in the Championship," said former Manchester United captain Robson who has been under pressure with the mid-table Blades.

Sheffield United, after City's Elano hit the post and had a curling shot saved by Paddy Kenny, doubled their lead when Stead scored from 12 yards after seizing on a loose ball.

Eriksson's decision to bring on Sturridge after half-time was rewarded when, with his first touch of the game, he struck a left-foot volley off the underside of the crossbar.

At Old Trafford, Cristiano Ronaldo took his tally for the season to 25 goals as he scored twice in a come-from-behind victory.

Spurs, who earlier in the week thrashed Arsenal 5-1 to book their place in the League Cup final, had to play the final 21 minutes with 10 men after defender Michael Dawson was sent-off for deliberate handball.

Ronaldo scored from the ensuing penalty and was on-target again two minutes before time in a match where Spurs striker Robbie Keane gave the visitors the lead in the 24th minute.

"It was a fantastic Cup tie," said United manager Sir Alex Ferguson.

"Tottenham had the best chances of the match but they didn't take them. We started well but then we seemed to be too relaxed. We allowed Tottenham a bit of momentum, they scored a fine goal and I think it roused us."

Spurs went ahead when Aaron Lennon moved past Patrice Evra and squared the ball to Keane who scored from close range as United conceded for the first time in five matches.

But United were level before half-time when veteran Wales winger Ryan Giggs shielded the ball from Lee Young-Pyo and so allowed space for Carlos Tevez to shoot beyond Spurs keeper Radek Cerny.

United's second goal came after keeper Edwin van der Sar's long punt downfield saw the ball travel from one box to the other and Dawson, under pressure from Wayne Rooney, was red-carded after pushing the ball away with his hand. Ronaldo scored from the spot after sending Cerny the wrong way.

Tottenham almost had an equaliser when Bulgaria striker Dimitar Berbatov hit the post six minutes from time with van der Sar beaten.

But Ronaldo then sealed victory when a deflected shot squirmed under Cerny's body in the 88th minute.

In Sunday's other fourth round tie Championship Cardiff City won 2-1 away to League Two Hereford.