National Bank Open: Marta Kostyuk vs Katherine Sebov

Platform comparison

Market context

Marta Kostyuk and Katherine Sebov are contesting a second-round women’s singles match at the National Bank Open in Toronto, with Kostyuk entering as the higher-ranked player and the listed favourite in pre-match data. The market’s 100% YES price implies the contract is effectively treating Kostyuk’s advancement as a near certainty, but the settlement mechanics still matter: if the match is not completed in a way that produces a winner, or is postponed beyond the seven-day window, the market can fall back to a 50-50 resolution rather than a straight player payoff. [1][2][3]

The historical frame is straightforward. Kostyuk beat Sebov in their only prior head-to-head meeting, a straight-sets win on hard court at Chicago in 2021, which lines up with the current surface and ranking gap. Match notes for this meeting also list Kostyuk ahead in the pair’s head-to-head record and show materially stronger season-long service and return indicators, which is the sort of profile that often underpins a one-sided pricing outcome in tennis markets. [7][14][2]

Traders should watch for anything that affects whether the match is played to completion before the settlement window closes: official tournament scheduling, court changes, weather delays, or a withdrawal/retirement announcement. The match had already been listed by tournament and live-score services as an upcoming Centre Court fixture, and later live feeds showed it in progress, so the key dependency is completion rather than initial scheduling alone. In a crypto-denominated market, the practical point is that the USDC outcome is binary only if the event resolves normally; otherwise the contract’s fallback path can override a strong on-court favourite. [3][15][5]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

Methodologically this overview focuses on on-chain pricing: Polymarket's live mid comes from the Polygon conditional-token order book and settles automatically in USDC. The other three venues — Kalshi, Betfair, Manifold — sit alongside as off-chain reference points so you can see how the contract translates across regulatory and settlement regimes.

Resolution & payout

Settlement is on-chain via UMA Optimistic Oracle. A proposer posts the outcome with a bond, a two-hour dispute window opens, then the smart contract lifts winning conditional tokens to 1 USDC and sends payments to holders' wallets automatically. No withdrawal fees beyond Polygon gas.

Off-chain venues (Kalshi, Betfair, Smarkets) settle in local fiat through bank-side clearing — faster than SWIFT, slower than on-chain. Manifold pays no real cash.

UK Frequently Asked Questions

Why USDC and not ETH or USDT?

USDC is the Polygon standard — audited reserves (Circle, monthly attestation), deepest order book, low gas costs. ETH volatility would distort probability quotes; USDT has thinner Polygon liquidity than USDC.

What does a transaction cost on Polygon?

Polygon gas is typically under $0.01 per transaction. A full trade cycle (Approve + Order + Fill) totals around $0.03 — compared to $5-50 on Ethereum mainnet.

Is Polymarket legal in the UK?

Polymarket is accessible to UK traders but is not UKGC-licensed. It operates under US CFTC jurisdiction. UK residents face no domestic legal prohibition on using it, but UKGC consumer protections do not apply. For UKGC-regulated alternatives, Betfair Exchange and Smarkets offer similar prediction-style markets.

Do I pay tax on prediction market profits in the UK?

UKGC-licensed platform profits (Betfair, Smarkets) are typically tax-free gambling winnings for UK individuals. Polymarket profits involve USDC crypto transactions, which HMRC treats as Capital Gains Tax events. Keep full transaction records and report via Self Assessment if gains exceed £3,000 per tax year.

How do I deposit on Polymarket from the UK?

UK traders typically fund Polymarket via Coinbase UK, Kraken or Revolut — buying USDC with GBP and transferring to a Polygon-compatible wallet (MetaMask, Coinbase Wallet). Polymarket's onboarding walks you through the bridging process. Typical GBP-to-USDC conversion costs 0.5–1%.