British No 1 Johanna Konta suffered a second-round exit at the hands of world No 97 Bernarda Pera at the Madrid Open on Tuesday.
Konta made 34 unforced errors as she went down 6-4 6-3 in the Spanish capital to the Croatian-born American.
The Briton had claimed an encouraging win over Magdalena Rybarikova earlier in the week, but 23-year-old Pera was more aggressive on the red dirt in the Spanish capital to brush her aside.
Fourth seed Elina Svitolina slumped to a surprise loss to Spaniard Carla Suarez Navarro.
The Ukrainian world No 4 will now prepare for the defence of her title in Rome next week, while Suarez Navarro will face Pera in round three after a 2-6 7-6 (7-3) 6-4 victory.
Also, third seed Garbine Muguruza came from a set down to defeat Croatia's Donna Vekic 2-6 6-4 6-1.
The two-time Grand Slam champion and home favourite was in trouble when she dropped serve in the fifth game of the second set, but won 10 of the next 12 games to race to victory.
The Masters 1000 Series continues throughout this week with our coverage of the ATP Madrid Open on Sky Sports Arena. Check listings for starting times.
Keep up to date with the latest on sky.mnosports.com/tennis with news, previews, live blogs, reports and expert analysis. On the move? Head to our app for mobile devices and iPad, or follow our Twitter account @SkySportsTennis to join in the conversation.
Never miss the big kick-off or have to deal with interrupted games or low quality streams with a NOW TV Sky Sports Pass. You'll get exclusive coverage of the Premier League, Sky Bet EFL, EFL Cup and loads more starting from just £7.99. No contract.