# O'Leary loses IBO super‑lightweight title to Chamberlain

> Live situation record from CLSTR: https://clstr.news/situations/pierce-oleary-ibo-title-defense
> Updated: 2026-08-01T22:41:41.000Z. Sources: 18. Developments: 3.

The IBO super‑lightweight world title bout at Dublin’s 3Arena on 1 August 2026, originally billed as Pierce O’Leary’s defense against Mark Chamberlain, ended with Chamberlain winning by a tenth‑round stoppage. After an early knock‑down spree that saw O’Leary down twice, the Irish champion rallied to drop Chamberlain in round 7, but Chamberlain recovered, regained control and forced a referee halt at 1:37 of round 10. The result gave Chamberlain an 18‑1‑1 record with 13 stoppages and handed O’Leary his first professional loss, moving his record to 19‑1. The event, streamed live on DAZN and attended by roughly 8,000 fans, also featured a vacant WBA continental super‑welterweight title fight between Ben Fail and Craig O’Brien and several Irish‑focused match‑ups. Former world champion Steve Collins praised the night’s atmosphere and its significance for Irish boxing despite the upset.

## Claims

- Mark Chamberlain defeated Pierce O'Leary by stoppage in the 10th round. (corroborated by 4 sources)
- The bout took place at Dublin's 3Arena. (corroborated by 4 sources)
- Mark Chamberlain won the IBO junior welterweight title. (corroborated by 4 sources)
- Chamberlain knocked O'Leary down twice in the first three rounds. (corroborated by 4 sources)
- O'Leary knocked Chamberlain down in the seventh round. (corroborated by 4 sources)
- The referee stopped the fight at 1:37 of round 10. (single source)
- Chamberlain's record improved to 18 wins, 1 loss, 1 draw with 13 stoppages. (single source)
- O'Leary's record fell to 19‑1 after his first professional loss. (single source)

## Timeline

### 2026-08-01: Mark Chamberlain captures IBO junior welterweight title in Dublin

Mark Chamberlain stopped Pierce O'Leary in round 10 at Dublin’s 3Arena, claiming the IBO junior welterweight title; Chamberlain improves to 18‑1‑1, O'Leary records his first loss.

10 sources. https://clstr.news/cluster/mark-chamberlain-captures-ibo-junior-welterweight-title-in-dublin

### 2026-07-30: Pierce O'Leary Defends IBO Super‑Lightweight Title Against Mark Chamberlain in Dublin

Pierce O'Leary defended his IBO super‑lightweight title against Mark Chamberlain at Dublin’s 3Arena on Aug 1, 2026, after the bout was rescheduled due to Chamberlain’s chest infection; the fight aired on DAZN.

8 sources. https://clstr.news/cluster/pierce-oleary-and-mark-chamberlain-to-clash-at-dublins-3arena-on-august-1

### 2026-07-28: Pierce O'Leary Defends IBO Super-Lightweight Title at Dublin's 3Arena

Pierce O'Leary will defend his IBO super‑lightweight title against Mark Chamberlain on 1 Aug 2026 at Dublin’s 3Arena, aiming to follow Katie Taylor’s legacy.

3 sources. https://clstr.news/cluster/pierce-oleary-defends-ibo-super-lightweight-title-at-dublins-3arena

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Cite as: O'Leary loses IBO super‑lightweight title to Chamberlain. CLSTR, https://clstr.news/situations/pierce-oleary-ibo-title-defense