Ferguson will be hoping he is still loved and needed by the Red Devils at the end of the season after turning 64 today.
But he will have wanted nothing more than this emphatic win over United's local rivals to stay 11 points behind Premiership leaders Chelsea.
For Ronaldo, 2005 has been a miserable year with the death of his father, police questioning over allegations of rape and a burglary at his home, but at least it went out on a high note for the young Portuguese star.
He was sharp and caused Bolton several problems - not least with his two goals and two shots against the post.
Up front, the magnificent Wayne Rooney combined well with Saha who scored his first Premiership goal of the season.
Darren Fletcher and John O'Shea provided a combative paring in the centre of midfield while Rio Ferdinand was dominant at the heart of United's defence.
Bolton's hopes of stifling United with their five-man midfield supporting lone striker Kevin Davies was undone as early as the eighth minute when the hosts went ahead. Key men Stelios Giannakopoulos, Jay-Jay Okocha and captain Kevin Nolan were well below their best.
United had already probed Bolton's defence before they took the lead, Ryan Giggs and Kieran Richardson linked superbly down the left.
Richardson provided the cross into the centre of the Bolton box and Bruno N'Gotty, under pressure from Saha at the near post, saw the ball go into his own net off his knee.
United could have increased their lead in the 29th minute when a one-two between Giggs and Rooney ended with the England man producing a fierce 20-yard shot which was well-saved by Bolton keeper Jussi Jaaskelainen.
But, out of the blue, came Bolton's equaliser four minutes later. Okocha's long throw-in from the left was headed on by Abdou Faye at the near post and United's defence went walkabouts as Gary Speed found himself unmarked on the far post to head home from four yards.
United were denied an immediate reply when Rooney carved an opening for Saha whose shot was well saved by Jaaskelainen at close range.
United went even closer after 35 minutes. Giggs' perfect cross from the left found Ronaldo on the far post and he allowed the ball to fall before hitting a right-foot volley from ten yards which crashed against the post.
Luck came United's way a minute before the interval. Bolton's central defender Tal Ben-Haim headed a long ball out of the United defence over his head without looking. Saha pounced to collect the ball 40 yards out and raced on into the Bolton box before rounding Jaaskelainen and scoring with a shot from almost on the byline.
The second half began quietly, but Bolton's expected onslaught never materialised. Ronaldo must have felt that it was not going to be his day when his clever one-two with Saha ended with his shot from the edge of the box rebounding off the foot of a post. But, four minutes later, United were 3-1 ahead and this time everything went right for Ronaldo.
Rooney and Saha played the perfect one-two and Rooney emerged on the left side of the penalty area with his cheeky chip to the far post setting up Ronaldo to score with a right-foot shot from close range.
Jaaskelainen saved well from Fletcher's 20-yard drive and United completed the scoring seconds into injury time.
Ruud van Nistelrooy, a 73rd minute substitute for Saha, swept the ball for Ronaldo on the right. The young Portugal star cut into the box, beat the flat-footed N'Gotty on the way, before rolling his left-foot shot home from 12 yards.