Britain's new number two Heather Watson began the Aegon Classic in Birmingham in fine style with a 6-3 7-5 win against 15th seed Chanelle Schneepers.
The 19-year-old Watson, who made the second round of the French Open, transferred her top form to the grass to shock the South African on Monday.
Britain's Samantha Murray lost in the first round 7-5 6-1 to Anna Tatishvili.
Watson on 26 May but rose to a career-high 93 in the world rankings.
She will next face Japan's Misaki Doi or Edina Gallovits-Hall for a place in the third round.
Kanepi is the top seed for the Birmingham event that runs from 6 - 12 June.
Murray's defeat meant she missed out on the chance of a second-round clash with former world number one and second seed Ana Ivanovic.
Following her success at Roland Garros in May, Guernsey's Watson overtook Anne Keothavong to become the new British number two, behind 74th-ranked Elena Baltacha.
Two Britons who did not fare so well on the opening day in Birmingham were Emily Webley-Smith, who went down 6-4 6-3 to 14th seed Magdalena Rybarikova.
While Mel South lost 6-4 6-1 to Rebecca Marino, the Canadian 13th seed.
Maria Sharapova, a winner in 2004 and 2005 and twice runner-up, and Marion Bartoli - beaten semi-finalists in the French Open - both withdrew from the tournament after their exertions in Paris.
The Birmingham tournament immediately precedes the grass court tournament at Eastbourne which runs from 12-19 June, with Wimbledon starting a day later.