Possible Clues:

• It may call for a snap decision at Aintree
• Dead heat at Belmont, say
• O
• Really close outcome in a race
• Shot over angle's defended in exciting climax
• Very tight end to a race
• Closest possible end to a race
• Close race's ending, or a hint to 17-, 26- and 45-Across
• Conclusion of a neck-and-neck race
• Very close horse race