Defending champion Carlos Alcaraz through to fourth round in Miami

The 19-year-old Spaniard returned to the world number one spot last week.

Carlos Alcaraz beat Dusan Lajovic 6-0 7-6 (5) in Miami (Marta Lavandier/AP) (AP)

Defending champion Carlos Alcaraz moved into the fourth round of the Miami Open after seeing off Dusan Lajovic in straight sets.

The 19-year-old Spaniard, who returned to the world number one spot last week as he lifted the trophy in Indian Wells, emerged with a 6-0 7-6 (5) victory from a contest lasting just over 90 minutes.

The first set accounted for 32 minutes of that as Alcaraz broke his Serbian opponent in the opening game and did not let up en route to a whitewash.

In the second he suffered his first break of serve at 5-4 before going on to secure victory via a tiebreak.

Alcaraz said in quotes on atptour.com: “I feel fast on court, I am moving well.

“I am happy with the variety I am playing (with). Lots of shots. I am enjoying every single second out there.”

Alcaraz, who will prevent Novak Djokovic from replacing him at the top the world rankings if he retains the Miami title, will next face Tommy Paul, a 6-3 7-5 victor over Alejandro Davidovich Fokina.