Gone was the inconsistent play and missed penalties from Mbappe during his first months with Madrid following his move from Paris Saint-Germain.
The France captain has started pouring in goals with back-to-back multi-goal matches and has Madrid in pole position with Atletico Madrid and Barcelona stalled.
The game between the front-runners and the bottom side lived up to its billing as a mismatch.
Valladolid could draw only one save from Thibaut Courtois, in the opening moments. It was all Madrid the rest of the way.
Madrid's fourth straight win in the league combined with Atletico Madrid's 1-1 draw with Villarreal let Carlo Ancelotti's side open a four-point gap over their city rivals.
Barcelona are in third place at 10 points back before hosting Valencia on Sunday.
Mbappe swept in Madrid's first goal on the half-hour mark after a flowing team attack weaved the ball through a packed Valladolid area that culminated in Jude Bellingham's assist for the France star.
He made it a double in the 57th by finishing off a counterattack after Federico Valverde intercepted a Valladolid pass. Mbappe took a pass by Rodrygo and rifled in a low strike from the left side of the box.
Kylian Mbappe celebrates his second goal against Valladolid. (AP PHOTO)
Valladolid finished with 10 men after Mario Martín got a second booking in the 90th for a foul on Bellingham, sending Mbappe to the spot for his third goal.
In the league, Mbappe now has 15 goals, second only to Robert Lewandowski's 16 for Barcelona.
Atletico's stalemate with Villarreal came a week after a shock 1-0 loss at Leganes.
Gerard Moreno, Villarreal's top scorer in club history, made it 120 goals for the Yellow Submarine in the 25th minute after the striker converted a penalty he earned when fouled by Reinildo.
Atletico coach Diego Simeone rested Antoine Griezmann and midfielder Rodrigo de Paul for the first half. Then he made three changes at halftime, sending on De Paul and winger Samu Lino to kickstart his sluggish attack.
The moves paid off as the hosts pressed Villarreal into its box, and Lino rammed in a 58th-minute equaliser.
Simeone sent Griezmann on immediately after and the action stayed in Villarreal's area except for two chances for Villarreal's Ayoze Pérez, who replaced Gerard.
Cedric Bakambu headed in a stoppage-time winner to grab Real Betis a 1-0 victory at 10-man Mallorca.
Mallorca had opportunities until Omar Mascarell received a direct red card for a studs-first tackle of Betis' Jesús Rodríguez in the 73rd.
The win came while Betis secured a loan deal for forward Anthony from Manchester United.
Goalkeeper Joan García made three saves to deny Sevilla standout Dodi Lukebakio and help Espanyol grind out a 1-1 draw at Sevilla.
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