Ronaldo, who returned to United from Juventus last month, opened the scoring on the stroke of halftime, while Newcastle drew level on 56 minutes.
Ronaldo restored United's lead with his second -- showing power and speed as he latched on to a through ball from Luke Shaw and fired through the keepers legs before reeling off to celebrate with his team mates in front of an ecstatic Stretford End.
Fernandes made sure of the three points in spectacular style 10 minutes from time, while substitute Jesse Lingard added to the celebration with a well-taken shot from inside the box after good work from Pogba.
Chelsea beat Aston Villa 3-0 for their 600th Premier League victory to move joint top of the standings alongside Manchester United after Romelu Lukaku and Mateo Kovacic scored for the first time at Stamford Bridge.
Lukaku, who previously played for United, Everton and West Bromwich Albion, had never scored at the ground -- even during his first spell with Chelsea. But he got off the mark in his 15th appearance at the stadium when he opened the scoring.
Bernardo Silva scored the only goal as Manchester City grabbed a vital 1-0 win at Leicester City to be third on the table, while Leicester are ninth.
The mood in north London will have changed as Tottenham were beaten and Arsenal won.
Odsonne Edouard scored twice on his debut to help Crystal Palace to a comprehensive 3-0 win over 10-man Tottenham Hotspur at Selhurst Park.
Spurs centre back Japhet Tanganga was shown a second yellow card in the 58th minute for a foul on Jordan Ayew, five minutes after the defender was adjudged to have illegally blocked winger Wilfried Zaha.
Matters got worse for the visitors as Palace were awarded a penalty when Ben Davies handled from a Conor Gallagher cross in the 75th minute, and Zaha dispatched the spot-kick past Hugo Lloris.
Earlier, Spurs, who were without the injured Son Heung-min and had to take off Eric Dier due to a suspected ankle problem after just 12 minutes, struggled to get going in attack and had just one shot on target in the game.
Spurs, who were top of the table, drop to fifth while Palace moved up to 11th place.
Arsenal moved off the bottom of the standings and scored their first goal of the campaign after captain Pierre-Emerick Aubameyang's scrambled 66th-minute effort gave them a 1-0 home win over Norwich City.
Mikel Arteta's side produced an improved performance after their opening three defeats but were made to work hard by a rugged Norwich side before Aubameyang, who missed two first-half chances, broke the deadlock.
The result lifted Arsenal to 16th place on three points from four games while Norwich, who are still looking for their first point of the season, slipped to the bottom of the table.
Southampton were held to a scoreless draw by ten-man West Ham United after the Londoners had striker Michail Antonio sent off in second-half stoppage time for a clumsy challenge.
The draw meant West Ham slipped to sixth place in the standings on eight points while Southampton are 14th on three points.
Leandro Trossard scored a late winner with a curling shot from the edge of the box as Brighton & Hove Albion secured a 1-0 victory over wasteful Brentford in a lively game at the Brentford Community Stadium.
The Belgian forward picked up the ball on the edge of the box, skipped away from two defenders and curled his shot into the bottom corner to stun the home fans, who had watched their side waste a number of opportunities to win the game.
Brighton climbed to fourth in the table and Brentford are 10th.
Wolverhampton Wanderers claimed their first three points of the season with a 2-0 win at Watford.
Wolves, who lost their first three games 1-0, moved out of the relegation zone and up to 13th in the standings, two places above Watford.