National Bank Open: Marta Kostyuk vs Katherine Sebov

Platform comparison

Market context

Polymarket is pricing this contract at **100% YES**, which means the market is behaving as if Marta Kostyuk will advance against Katherine Sebov under the match’s current live state on Polygon. On Polymarket, buyers pay USDC for conditional tokens, and the contract only settles once the event outcome is known; if the match is abandoned, tied, or left unresolved beyond the market’s seven-day grace period, the contract can still resolve to 50-50 rather than a clean winner. [1][3]

That pricing is consistent with the underlying tennis context. Kostyuk is the higher-ranked player by a wide margin, listed around world No. 11, while Sebov is a wildcard ranked near No. 231, and their only prior meeting was won by Kostyuk in straight sets at Chicago in 2021. Historical head-to-head alone is not decisive, but in this pairing it supports the view that the favourite is carrying the much more plausible advance outcome. [2][4][9]

For traders, the key watchpoints are simple: official scoreboards, match completion status, and any tournament scheduling change that might push the finish outside the market’s settlement window. The National Bank Open match notes show the contest was scheduled for 4 August 2026 in Toronto, and live match pages indicate it has been underway, so the main risk is not the pre-match setup but whether play is completed and formally recorded before Polymarket’s deadline. If the match is interrupted, the exact wording of the contract matters more than the raw scoreline, because advancement, retirement and no-contest scenarios can resolve differently. [3][7][9]

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

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

FAQ

How does resolution work?

Through the UMA Optimistic Oracle on Polygon: a proposer submits the outcome, a two-hour challenge window opens, and USDC payouts settle automatically once the result is final.

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.