Robson had been determined to land a big name striker to lift spirits at Bramall Lane following relegation from the Premiership and got his man on a four-year contract.
Blackburn had expressed interest and Middlesbrough and Birmingham were also monitoring the race but United made the best offer and Robson's persuasive talking did the rest.
The manager said: "I'm delighted. We've got a strike force now that ranks as the best in the Championship. It's a signal of our intention to return to the top flight."