Related Clues:

• Reliable pro
• Get top marks on
• It's not returnable, in tennis
• Go-to person
• Versatile playing card
• Leader of the pitching staff
• Versatile blackjack card
• Part of a 23-Across
• Top serve
• Unhittable serve
• One in play?
• Single, slangily
• Losing streak breaker, say
• Untouchable service
• Versatile card