NICK Gubbins got a monkey off his back when he celebrated a maiden first-class hundred at Lord's as Middlesex battled throughout day three to reach 407 for 9 and overhaul Somerset's first innings 376 in the Specsavers County Championship.

While there was ecstasy for Gubbins, however, and a first-class best for Middlesex of 85 by Paul Stirling, there was agony for his fellow opener Sam Robson who failed by just one run to hit four successive hundreds at Lord's when he was out for 99 in the Division One match.

But, less than quarter-of-an-hour later, Gubbins joyously completed his long-awaited century, in his 39th innings and 23rd first-class match, and after being dismissed on three previous occasions in the 90s.

The 22-year-old left-hander leapt in the air, with both arms raised, when he reached three figures with a driven boundary off Jim Allenby wide of mid-on - and his burgeoning career will surely now kick on.

He was eventually dismissed soon after lunch for a near five-hour 109, with Marcus Trescothick taking a sharp chest-high catch slightly to his left at slip as Gubbins flashed at Allenby, but this season the former Radley College pupil already has 376 championship runs from eight innings.

In 2015 he managed just 354 from seven four-day appearances, at an average of 27.23.

Robson was bowled by left-arm spinner Jack Leach, trying to cut, and his opening partnership of 198 with Gubbins also failed by a single run to match Middlesex's first-wicket record against Somerset - the 199 put on by Jack Robertson and Syd Brown at Lord's in 1951.

Right-hander Robson, whose previous three championship innings at Lord's were 114 not out, 106 and 231, had resumed on 67 in Middlesex's overnight 139 without loss and batted overall for four hours, facing 206 balls and hitting 14 fours.

Before snaring Gubbins, who had been on 65 overnight and hit 15 fours from 234 balls with some eye-catching drives down the ground, medium pacer Allenby had also had Dawid Malan caught at slip for five and, armed with the second new ball, Tim Groenewald pinned both Adam Voges and John Simpson lbw,f or 18 and 10 respectively, in an hour after lunch that seemed to have suddenly tipped the contest Somerset's way.

From 252 for 5, however, Middlesex were revived by Stirling who, in stands of 49 and 71 with James Franklin and Ollie Rayner, guided them into the lead.

Stirling hit a six and 11 fours in a responsible 132-ball effort after seeing Franklin edge Leach to slip for 23 and Rayner depart for 26 when he was leg-before to the same bowler.

Stirling also fell leg-before to the 25-year-old Leach, who bowled accurately and well to finish with 4 for 64 and might have been given even more than his 29 overs by Chris Rogers, the Somerset captain.

Gubbins revealed afterwards that it was his father Richard's 59th birthday today -and that both his parents has "secretly" made it to Lord's to watch in case he did convert his overnight 65 into a maiden first-class hundred.

"We're going out to dinner tonight as a family so it's great to get my first hundred on my Dad's birthday," said Gubbins. "I'm delighted to get the hundred finally - yes, three previous scores in the 90s was something that was playing on my mind.

"It's been tough getting to this landmark, but it's also a dream come true to get my first hundred at Lord's where I've been coming since I was a boy.

"It's also great to bat with Sam (Robson) at the top of the order. He's in great form and sadly didn't quite get his hundred today, but we complement each other and obviously we're also a right and left hand combination.

"I've been very lucky in my time in the Middlesex team. I started out opening with Chris Rogers and now it's Sam. I've also batted a lot with Nick Compton, so I've had a lot of great talent and experience around me."

Middlesex also feel there is still a chance they could beat Somerset as they take a 31-run lead into the final day.

"There's a bit in the pitch and we'll try to get a few more runs tomorrow and then put them under pressure with the ball," added Gubbins.