The 18-yo earns his 2nd top-5 win and advances to the MiamiOpen quarterfinals with a 7-5 6-3 win over Tsitsipas.
The Spaniard looked like the more experienced player in his 7-5 6-3 victory, delighting the crowd with his amazing speed and shot-making.
After being broken and falling to 2-5 in the opening set, the 18-year old fought back to stun the Greek star. Displaying composure and confidence that misrepresented his youth, Alcaraz reeled off five consecutive games to win the first set.
With momentum squarely on his side, Alcaraz obtained an early break in the second set to race to a 2-0 lead. Despite Tsitsipas' best attempts, the third seed was unable to weather the Spanish storm. Alcaraz saved all three break points faced in the second set, before sealing victory with a sublime drop-shot.
The World No.16 has been on a tear over the last two weeks, reaching the semifinals at Indian Wells where he fell to Rafael Nadal in a close three-set encounter. Alcaraz will face the winner between Taylor Fritz and Miomir Kecmanovic, as he advances to his second straight ATP Masters 1000 quarterfinal.