A rider and two spectators have been killed following a crash during the Senior race at the centenary Isle of Man TT meeting on Friday.
McGuinness' Senior win was his 13th TT victory
Marc Ramsbotham, 34, died instantly in the incident at the 26th milestone section of the course while a spectator was pronounced dead at the scene.
Another spectator died in hospital and two marshals were injured.
Lancashire's John McGuinness became the first rider in TT history to break the 130mph barrier when he won the race.
Isle of Man TT organisers said an investigation had been launched into the circumstances of the accident.
McGuinness, who also won the Superbike event on Monday, beat his own record by clocking 130.35mph on the second lap.
McGuinness finished 33 seconds ahead of Guy Martin with Ian Hutchinson third.
Ian Lougher was fourth and he was followed home by NI's Adrian Archibald, Conor Cummins, Steve Plater and Michael Rutter in eighth.
Pre-race contenders Martin Finnegan, Bruce Anstey and Ryan Farquhar all retired on the opening lap.
Success in the final race of the centenary meeting takes McGuinness to 13 TT wins.
The first four finishers were all riding Honda machines.