Dec 17 (Reuters) - Thailand's Kunlavut Vitidsarn beat Jonatan Christie while South Korea's An Se-Young battled past Putri Kusuma Wardani on a contrasting opening day for the top-ranked players at the badminton World Tour Finals in Hangzhou on Wednesday.

Vitidsarn, the men's world number one, got off to a fast start and dominated the exchanges throughout his 21-10 21-14 group stage victory over Christie for his sixth win against the Indonesian player.