Possible Clues:

• No racehorse alive is one!
• That's for sure
• You're going to be born and you're going to die - that's for sure!
• Presumably you could put money on him being late for an open-and-shut case
• Racehorse that's sure to have the most life, paradoxically
• No more, for sure, and that's no lie
• Late for sure
• Created dainty confection - a sure-fire winner
• To be sure, that's 15 across