The 59th career hat-trick of Ronaldo's career was just his second for United and a first in 14 years as his second spell has failed to match the hype around his signing in August, AFP reported.
United go into Tuesday's finely balanced Champions League last-16 tie against Atletico Madrid, after a 1-1 draw in the Spanish capital, knowing European glory is their only remaining chance of silverware this season.
Ronaldo has tended to save his best for the Champions League this season, scoring six goals in the group stage just to ensure United did not suffer the ignominy of a group stage exit for the second consecutive season.
However, his subdued performance as a frustrated and isolated figure up front the Wanda Metropolitano three weeks ago was more reflective of the problems Ralf Rangnick has faced during his interim spell as United manager.
The German is credited as the godfather of the high-energy, pressing style of play that has inspired the likes of Jurgen Klopp and Thomas Tuchel to go on to be Champions League winners as coaches.
Rangnick has not been able to implement the same verve to United, much of which has been blamed on a 37-year-old Ronaldo's inability or unwillingness to press.
The Portuguese has also been pointed at as the source for stories of dressing room disquiet that seem to leak out after every poor result.
Amid reports he was set to be dropped for last weekend's Manchester derby, Ronaldo jetted back to his homeland to rehab a hip injury that was given as the official reason for missing a 4-1 thrashing at the Etihad.
Rangnick joked that maybe he should sanction that trip more regularly after Ronaldo returned to Manchester in scintillating form to put Spurs to the sword.
But he also did not hold back in his assessment of Ronaldo's work off the ball in recent weeks.
"Today he showed for sure that he is physically capable to do that," Rangnick said of Ronaldo's defensive contribution.
"We also have to admit that it has not always been like that in the past weeks and months.
"Today showed exactly that he is still in physical shape to perform at that level."
Ronaldo's performance impressed the watching Tom Brady as the seven-time Super Bowl winner told his fellow superstar to "keep playing" as they embraced on the Old Trafford pitch after the game.
Whether he stays for the second year of his contract at United will depend heavily on if the Red Devils make it into the Champions League next season.
Into the twilight years of his career, he can ill afford a season off the biggest stage where he shines brightest.
Atletico know that only too well. Between 2014 and 2019, Ronaldo was on the opposite side for all five of their exits in the knockout rounds of the Champions League, twice inflicting the ultimate blow in final defeats to Real Madrid.
Ronaldo's treble on Saturday set another goalscoring record as he now has the most goals in men's professional football according to FIFA's records with 807.
Only Sevilla have suffered more in that total than the 25 Atletico have conceded.
As United's struggles have laid bare, Ronaldo may not be the force he once was.
But he is still the one Diego Simeone's men will fear most coming back to haunt them on the big occasion.