National Bank Open: Elise Mertens vs Naomi Osaka

Platform comparison

Market context

The match is a straightforward Osaka–Mertens hard-court head-to-head, and the market’s 0% YES print is the sort of extreme number that usually reflects a stale feed, an already-processed result, or a platform issue rather than a live assessment of a still-pending tennis fixture. Their recent meetings have been competitive enough to matter for modelling: Osaka leads the rivalry 4-3 across seven professional matches, but Mertens won their most recent meeting in Toronto in August 2024 on hard court, 6-3 6-4.[3][13] That recent split is useful for programmatic trading because head-to-head alone will not cleanly separate the players; bots typically need to weight surface, tournament stage, and recency rather than rely on an aggregate rivalry count.[3][11]

Comparable recent data point in both directions. Osaka beat Mertens in Bad Homburg in June 2026, and the match stats there showed Osaka with a strong serving edge, including 7 aces and 86% of first-serve points won.[4][7] Earlier, their 2024 National Bank Open match in Toronto ended with Mertens winning in straight sets, with the event site recording Mertens taking 66% of break points and 54% of total points.[11] For a power user automating entries, the key catalyst is whether the match is actually scheduled and starts on time: if it is cancelled, delayed beyond seven days, or left unresolved, the market settles 50-50 under the rules; if it begins and one player advances, the winner should be the clean settlement trigger. Use schedule checks and official draw updates rather than only score feeds, because the settlement logic depends on completion status as much as on the eventual score.

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.

UK Frequently Asked Questions

Where can I trade this market with the lowest fees?

Polymarket is geo-blocked in the US/UK/EU. The easiest 0%-fee broker into the same order book is Polymarket Bot UK. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

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.

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%.