The 34-year-old Welshman joined a select band of players, including Bobby Charlton, Denis Law and George Best to have hit a century for the Red Devils.
Giggs, who made his league debut for United back in March 1991, seems to get better with age.
This was vintage Giggs, who left the field to a standing ovation in the 64th minute after scoring one and being denied a second by the foot of a post.
Giggs broke the deadlock in the 40th minute of a game played on a sodden Old Trafford pitch with the rain swirling around the stadium throughout.
The move began when Anderson found Patrice Evra on the left side of the Derby box.
He threaded the ball back into the penalty area while Cristiano Ronaldo put a fierce 25-yard shot and, although Derby goalkeeper Stephen Bywater blocked his effort, Giggs followed up to side-foot the rebound home from eight yards.
United made it 2-0 in first-half injury time as Ronaldo chipped a 25-yard free-kick to the left of the Derby box inside the penalty area to Anderson.
He helped the ball on to Carlos Tevez, standing near the penalty spot and, although the Argentinian had a comic moment when he missed his first shot completely, he soon recovered to place his second effort into the roof of the net from 12 yards.
Tevez added United's third goal on the hour when he raced on to Wes Brown's clever pass from the right and dispatched the ball into the bottom corner of the net with a shot from just inside the box.
Ronaldo completed United's scoring deep into injury time.
Tyrone Mears was harshly adjudged to have brought down Ronaldo in the box when the United man looked to fall over the legs of the Derby substitute.
Referee Chris Foy pointed to the spot and, after a shimmy, the Portuguese star buried the ball into the bottom right corner of the net from the resulting penalty.
Wayne Rooney hit the post with an audacious chip after being put clear by Giggs' glorious 40-yard through ball and the Welsh maestro also struck a post with a superb left-foot volley from Brown's cross.
But spare a thought for Derby as they battled hard all afternoon and were rewarded with their first away goal in the Premier League this season when substitute Steve Howard bundled home Mears' right-wing cross off his chest from six yards.