Of the counties occupying the top four places in the First Division table, Durham's title credentials are seen as the least convincing, yet so long as England do not decide to factor Graham Onions into their Ashes plans, they will remain at least dangerous outsiders.
They have made life difficult for Middlesex, who went into the latest round of matches as leaders yet spent much of the second day here in a grim battle to stay in contention. Onions, under the watchful eye of England selector James Whitaker, took five wickets in an innings for the 18th time in his career, and Middlesex, at one stage 35 for 5, were relieved that Neil Dexter and John Simpson applied themselves for long enough to see off the new ball.
Their stand of 68 in just over an hour during the afternoon session provided the opportunity for James Harris to chip in with a valuable 37 and trim Durham's lead to 63.
After losing both openers on the first evening, Middlesex knew they would struggle to come close to Durham's 259 and a regular stream of squally, wintry showers made their task all the more difficult as play started and stopped five times. It played into the hands of Onions, whose short, sharp bursts left Middlesex four down at lunch. He had Joe Denly well taken by Scott Borthwick at second slip and pinned Dawid Malan leg before, although umpire Martin Bodenham needed several seconds to deliberate ahead of announcing his verdict.
An hour was lost in the morning. The afternoon was less chaotic and though Middlesex lost a fifth wicket when Ben Stokes, during an inconsistent spell, trapped Tom Smith with a full length ball to end a doughty effort by the nightwatchman, Simpson punished Stokes for bowling too short with a succession of boundaries.
Onions found some extra bounce to force a miscue from Simpson and then had Gareth Berg caught at the second attempt by Paul Collingwood at first slip.
Dexter completed a half-century off 98 balls before Stokes jagged one back to have him caught behind off an inside edge.