Wayne Mardle has warned world darts champion Michael van Gerwen that he must remain fully focused throughout the defence of his crown.
The Dutchman survived a scare to beat Joe Cullen 3-1 in his first-round clash as the world number one goes in search of back-to-back titles at Alexandra Palace.
Mardle, a former semi-finalist at the tournament, says that 'Mighty Mike' cannot afford to 'go to sleep' against future opponents or he could pay the penalty.
"He should be dominating players that average 93, that's no disrespect to Cullen," he told Sky Sports News.
"He should be averaging 100, rolling along, turning them over and making them look sub-standard because he is that good.
"He goes to sleep far too often in matches. You never see Phil Taylor look perplexed - he might look frustrated or annoyed. Michael has an ability that we don't see very often but he has to use it time and time again."