user: Question: At the 2001 Davis Cup, what Opponent had less than 50 Aces?
Columns: ['Aces', 'Player', 'Opponent', 'Event', 'Sets']
Types: ['real', 'text', 'text', 'text', 'real']
Sample row: [113.0, 'John Isner', 'Nicolas Mahut', '2010 Wimbledon', 5.0]
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Aces" < 50.0 AND "Event" = '2001 Davis Cup';