National Bank Open: Marta Kostyuk vs Katherine Sebov

Platform comparison

Market context

Marta Kostyuk’s second-round match with Katherine Sebov at the National Bank Open is the type of fixture where the market can be read almost mechanically: ranking gap, head-to-head, and surface all point in the same direction. Kostyuk is listed around WTA No. 11, while Sebov is a wildcard ranked around No. 231, and the pair’s only prior meeting was won by Kostyuk in straight sets at Chicago in 2021.[5][10] That history helps explain why a 100% crowd-implied “YES” is effectively pricing a near-certain Kostyuk advance, even though tennis markets still need to respect retirement, walkover, or schedule risk rather than assume a completed match.[2][10]

For a power-user running this through tooling, the main job is not model-building so much as exception handling. Programmatically, the first checks are whether the match has started, whether an official result is posted, and whether the event remains within the settlement window if it is delayed or suspended; the market rules mean a non-played match, tie, or delay beyond seven days would force a 50-50 outcome, while a match that begins but is not completed resolves with the player who advances.[3] Recent match data on the tournament site also showed Kostyuk ahead in live statistics, reinforcing that the state of play matters more than pre-match narrative once the event is underway.[3]

Catalysts to monitor are straightforward: official order-of-play updates, any court-change notices, and in-match retirement or suspension signals from the tournament feed or live scoring layers.[3][1] If you are wiring alerts or copy-trading logic, the practical trigger is not the pre-match listing alone but confirmation that the scorebook reaches a final state, because the settlement logic changes materially if the match is not completed within the allowed window.[3]

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.

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.

Do I need to KYC for this market?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like Kalshi Fees trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.

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.