The 21-year-old striker, who replaced injured superstar Kylian Mbappe in the line-up, headed a 20th-minute opener and doubled Real's advantage early in the second half.
Raul Asencio headed the hosts further clear and, after Cucho Hernandez pulled a goal back for Betis, Gonzalo Garcia and Fran Garcia completed the scoring.
Atletico Madrid missed the chance to go third as they were held to a 1-1 draw at struggling Real Sociedad. Alexander Sorloth fired Atletico in front after 50 minutes, but Goncalo Guedes levelled five minutes later.
Elsewhere in LaLiga, goals from Iker Losada, Carlos Espi and Carlos Alvarez saw Levante move off the bottom with a 3-0 win at Sevilla.
They were replaced by Real Oviedo, who drew 1-1 at Alaves, while Girona moved out of the bottom three with a 2-1 win at Mallorca.
Inter Milan reclaimed top spot in Serie A as goals from Piotr Zielinski, Lautaro Martinez and Marcus Thuram eased them to a 3-1 win over Bologna, who replied late on through Santiago Castro.
A late brawl marred Napoli's 2-0 win at Lazio as first-half goals from Leonardo Spinazzola and Amir Rrahmani eased the visitors to victory.
Lazio had already had Tijjani Noslin sent off in the 81st minute before the tie erupted two minutes from time, with Pasquale Mazzocchi and Lazio's Adam Marusic also red carded after sparking a mass confrontation.
Moise Kean grabbed an added-time winner as Fiorentina moved off the foot of the table with a 1-0 win over Cremonese, while Torino strolled to a 3-0 win at Verona.
In Ligue 1, Ousmane Dembele fired the winner as Paris St Germain retained bragging rights in the French capital with a 2-1 win over Paris FC.
Desire Doue put PSG in front on the stroke of half-time and Dembele struck a deflected second less than two minutes after Willem Geubbels had levelled for the visitors from the spot.
Marseille had Arthur Vermeeren and Bilal Nadir sent off as they fell to a 2-0 home defeat against struggling Nantes, who claimed their first win in eight.
Brest beat bottom club Auxerre 2-0, a late winner from Noam Obougou gave Le Havre a 2-1 win over Angers and struggling Metz earned a 1-1 draw at Lorient.
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