Related Clues:

• Part of a winning combination
• One-third of XXX?
• See 13-Down
• See 23-Across
• Middle of a kids' game
• See 24-Across
• See 53-Down
• Part of X-X-X
• See 36-Across
• Part of OOO
• 'Hollywood Squares' square
• Tic-___-toe
• Center X or O
• Middle X of X-X-X
• It's 'twixt tic and toe