
Giggsy, 35, and mum Lynne Johnson, 51, were at the Champions League final in Rome when the swoop happened.
The Premier League star was said to be “hit for six” by the “unauthorised” bash at the £1.3million six-bed mansion.
Lynne and Giggs’s half-sister Bethany, 17, had travelled to watch United’s defeat on Wednesday.
Cops were alerted after Lynne’s 91-year-old next-door neighbour spotted men pull up in two cars at the pad in Worsley, Greater Manchester.
The widow said: “It was dark, I didn’t know what they wanted. I was frightened.”
A cop arrived to see two or three men and a woman run to the rear of the house and lock a door. But they vanished by the time officers got inside.

Raid ... Giggsy's mum Lynne
Cops allegedly found “drugs paraphernalia or items associated with drug-taking.” It is believed someone with their own key allowed revellers to get inside.
A police spokesman said: “We have found no evidence of a forced entry. We are waiting to speak to the occupant.”
A United source said: “This has hit Lynne and Giggsy for six. The fact drugs are allegedly involved makes this even more distressing.”
Giggsy, who lives near his mum in a £6million pad, talked anxiously on his mobile as he arrived back yesterday.
Trouble flared after United’s 2-0 defeat by Barcelona — with 11 people arrested in Manchester, 19 in Rome and 119 in Barcelona.
In Nigeria a United fan drove a minibus into a crowd of Barcelona fans, killing four people.