British number one Jack Draper lost in straight sets to Jakub Mensik at the Miami Open in his first match since lifting the Indian Wells title.
The 23-year-old, who has risen to a career-high seventh in the world rankings, was beaten 7-6 (7-2) 7-6 (7-3) by his Czech opponent in the second round.
Draper made a fine start, breaking Mensik with the first game of the match, but the 19-year-old levelled at 3-3 and was on top from then on.
The world number 54 sent down 21 aces, including four in taking the first-set tie-break.