Middlesex 196 (Compton 71, Onions 7-68) and 118 for 4 lead Durham 169 by 145 runs
Scorecard
On a day when 19 wickets fell at a heavily overcast Chester-le-Street, the one which got away proved costly for Durham.
Dawid Malan was dropped first ball and went on to reach 56 as Middlesex recovered from 29 for four to close the second day on 118 for 4 in their second innings, leading by 145.
As the sun threatened to put in an appearance in the final hour conditions eased and no wickets fell in the last 20 overs as Neil Dexter assisted Malan in the revival.
Durham also lacked support for Chris Rushworth, who took three for six in seven overs to equal Ottis Gibson's Durham record (set in 2007) of 80 first-class wickets in a season, 75 coming in the championship. He returned for three overs at the end without joy as Dexter moved on to 46.
Malan was put down at third slip by Gordon Muchall, spoiling a day on which he made his first home half-century in the Championship for four years. He was last out for 64 with Durham's total on 169.
The drop also marred Graham Onions' day as he had just had Nick Compton lbw to add to his 7 for 68 in dismissing Middlesex for 196 in their first innings.
Resuming on 141 for 5, Middlesex lost Dexter to the second ball of the day, completing Onions' second five-wicket haul of the season. The ball stood up off a good length to take the shoulder of the bat on the way to Ryan Pringle at fourth slip.
There were six slip catches in the innings, with Paul Collingwood holding four at first and Muchall taking a sharp one at third to give Onions his revenge after Toby Roland-Jones had taken 15 off his previous over.
When Durham batted Roland-Jones struck timber in both his first two overs, Mark Stoneman playing across a full-length ball to lose his leg stump before Graham Clark shouldered arms to one which didn't have to deviate much to hit off stump.
It became 7 for 3 when Collingwood was squared up by a ball from Tim Murtagh which lobbed off a thick edge for Compton to dive to his right at gully to hold an excellent catch.
Roland-Jones produced a beauty to have Scott Borthwick caught behind and two wickets in two balls for James Harris had Durham rocking on 51 for 6.
Debutant James Weighell began the recovery when he went in to face Harris's hat-trick ball and scored 19 off his first seven balls.
With Muchall briefly joining in the spree 31 came off 15 balls, but only four more were added before Weighell drove at Harris, bowling round the wicket, and lost his off stump for 25.
John Hastings helped Muchall add 30 before slicing to deep cover and there was a second wicket for Dexter when Rushworth fell to a sensational one-handed catch by Roland-Jones, diving to his left at mid-off.
Onions contributed 13 not out to a last-wicket stand of 39 before Muchall guided Murtagh to James Franklin at slip.
When Middlesex went in again Rushworth nipped the second ball back to take out Sam Robson's leg stump. Paul Stirling flashed wide of off stump and edged behind and Franklin was lbw when half forward.
Onions snared Compton, but with Hastings struggling Durham's lack of back-up allowed Malan and Dexter to ease Middlesex's jitters.
