National Bank Open: Kayla Day vs Coco Gauff

Platform comparison

Market context

Kayla Day and Coco Gauff are due to meet in the National Bank Open women’s singles, with the market about the chance of Day advancing. The crowd-implied probability is **0% YES**, but that is materially below the broader market read: Tennis.com’s preview model gives Day **13%** and Gauff **87%**, while BetUS has Gauff at **-1000** and Day at **+600**, which implies a clear favourite but not a total shut-out.[4][17]

That gap matters because tennis prediction pricing often swings between a “likely winner” and an “all but impossible” frame depending on whether traders are anchoring to ranking, form, or sportsbook vig. Gauff is the world No. 4 and the seed in this match, while Day is listed around No. 131 in the match notes and entered via qualifying, so the baseline consensus is heavily tilted towards Gauff, but not so far as to remove upset risk entirely.[8][2][13] Comparable early-round WTA 1000 markets are usually priced with some chance of a lower-ranked opponent taking at least a set, which is why a 0% market can diverge sharply from bookmaker lines even when the favourite remains overwhelming.[4][17]

For traders, the key catalysts are whether the match actually starts as scheduled and whether either player withdraws before first ball. The market rules mean a cancellation, tie, or delay beyond seven days resolves 50-50, so schedule integrity is as important as match strength.[Market description] Live listings on Yahoo Sports and Tennis.com still show the fixture as upcoming, which supports the assumption that the main binary is whether Gauff progresses or an upset lands.[1][4] Day’s recent three-set win over Diane Parry in Toronto also shows she is not entering cold, but the consensus still treats her as a major underdog against a top-four opponent.[20][13]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). That keeps the comparison honest — a single canonical probability across the row, with the venue-by-venue trade-offs spelt out in the columns next to it.

Resolution & payout

Settlement runs on-chain. Polymarket's contract logic separates YES and NO shares as conditional tokens; at resolution the winning share lifts to $1.00 and the losing one to $0. The outcome input comes from the UMA Optimistic Oracle, which secures against bad resolution with a bond + dispute window.

Once finalised, the smart contract pays USDC to the holders' wallets within minutes — no withdrawal fees beyond Polygon network gas. Kalshi settles in USD via CFTC clearance, Betfair in account currency net of commission, Manifold in play-money mana with no cash-out.

FAQ

Is this market available outside the US?

Polymarket itself is geo-blocked in the US/UK/EU. Always check the legal status of prediction markets in your jurisdiction before trading.

What's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

What does Polymarket cost to trade?

Polymarket itself charges 0% — the only cost is the Polygon network fee, typically under $0.01 per transaction. Off-chain venues like Kalshi or Betfair charge 2-7% commission.

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within minutes.

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.