From Jason Goodwin's popular history of the Ottoman Empire, Lords of the Horizons:
At the siege of Baghdad in 1683, when the Persians demanded the contest be decided by single combat, they put up a Herculean warrior from their ranks, and Sultan Mehmet IV took him on himself, splitting the Persian champion's mailed head in two with a single blow.
Big if true! But there's no source given, and, googling around, I can't even establish that there was a siege of Baghdad in 1683. I've found another couple of instances of the anecdote, but nothing with references.
Is there a reliable primary source for this story? If not, is it even plausible?