WIMBLEDON, England—After a week of showing her maturity at her first Wimbledon, 16-year-old Mirra Andreeva showed her inexperience on Monday.
The Russian qualifier, who had won all six of her matches on grass to reach the fourth round at the All England Club, let a big lead over 25th-seeded Madison Keys slip away in a 3–6, 7–6 (4), 6–2 loss on No. 2 Court.
Andreeva took the first set and led 3–0 in the second—winning nine of 10 games in one stretch—before Keys turned things around. Frustrated at one point, Andreeva threw her racket and received a warning from Swedish chair umpire Louise Azemar Engzell….