The two new boys initially agreed deals to join the club during the last season, and their contracts are now effective.
United fans have been excited by Chicharito’s promising displays at the 2010 World Cup. The talented striker hit two goals in four games for Mexico, including a superb late effort in his side’s last-16 defeat to Argentina at the weekend.
Chicharito is determined to succeed at Old Trafford. "My expectations are to do the best I can personally, to work, to learn, and to win many trophies," the 22-year-old said when the deal was first announced – to near-universal surprise – in April.
Defender Smalling, who played 18 times for Fulham last season, agreed terms on a four-year deal in January. The 20-year-old will link up with his new team-mates at Carrington next week as those players not involved in the World Cup return to training.
Chicharito will be given some time off after his exploits in South Africa and will meet his new team-mates for the first time during July's trip to the USA, Canada and Mexico.
Reds fans will likely get their first glimpse of the duo during the tour, and Sir Alex has confirmed Chicharito will play some part in the friendly against his former club Chivas.
For tour news, features and free videos, visit manutd.com/tour2010.