Essex 271 for 6 (A Cook 172, Westley 51, Gregory 4-58) trail Somerset 301 (Byrom 117, Overton 66, S Cook 5-76) by 30 runs

Alastair Cook produced an innings of the highest class to put Essex on top in the final of the Bob Willis Trophy at Lord's.

On a surface on which all his team-mates struggled for fluency, Cook made 172 - the 67th century of his first-class career and his 20th score in excess of 150 - to give Essex a good chance of establishing a first-innings lead. Essex's other batsmen contributed 91 between them.

But with only 36 more runs required to ensure a first-innings lead and barely 15 minutes left to play, Cook poked at one angled into him with the second new ball and edged to Craig Overton at second slip. It leaves the game intriguingly poised going into the fourth morning: Essex require 31 more runs with four wickets in hand to gain a potentially decisive lead.

The playing regulations of this competition state that, in the event of a draw, the winner of the trophy will be decided by the team with the highest first-innings score in the match. Therefore, if Essex are able to make 302, a draw will be enough for them. In this autumnal weather, that will be a concern for Somerset.

It speaks volumes for Cook's character that he was able to dig deep once more. Many players, returning to the county game after a long international career, struggle to rediscover the motivation that once drove them. But, fuelled by an abiding love for the game and the club he has represented, at one level or another, for more than 20 years, he once again provided the contribution his side required.

"Obviously it [my motivation] is not as it was a few years ago; that's one of the reasons why I'm not still playing international cricket," Cook said afterwards. "But it's a great club and it's great fun. I enjoy playing with this bunch of lads. A lot of them, I've played a lot of cricket with. If Ravi Bopara were still here, we played our first games together aged 12.

"I was scared when I retired from international cricket of walking away totally. Suddenly walking off at The Oval in 2018 - the last time I played - would have been a big hole to fill. And I've really enjoyed hanging out in the changing rooms at Essex. And we're a good side. It makes it better when you win.

"I'll definitely play next year and then we'll see how life is."

While it was a chanceless innings, it was not without some nervous moments. Twice in the opening 10 overs he played and missed; twice more he edged just short of the slip cordon. On 10, he sliced just over gully. Overton, the unfortunate bowler on the majority of occasions, let out a series of bellows of frustration.

From that point on, however, he looked in almost complete command. And, in a sure sign that he was somewhere near his best, there were a series of flowing cover drives that might have pleased a batsman as elegant as Ian Bell. With 13 fours hit in front of square on the off side - most of them through the covers - it was an performance which, for a while, evoked memories of his wonderful Ashes tour of 2010-11.

Perhaps it also tells us something about the relative pace of this pitch and the Somerset attack. As Michael Atherton has often remarked, county cricket is a game played largely below the hip; Test cricket a game played largely above. Had Somerset still had Jamie Overton available to them - he has recently moved to Surrey - he might have proved a point of difference.

It was, to some extent, a sobering day for Somerset. Their seamers had, before this game, taken their wickets at a cost of around 12 apiece this season. Only one side had scored more than 200 against them and the opposition's average score was 119. They are, without doubt, an admirable attack.

But those figures do reflect some helpful surfaces and brittle batting line-ups. Here, on a higher-quality pitch and against a high-quality batsman, they were made to work substantially harder. It was a reminder, perhaps, that we have to be careful about judging bowlers' suitability for international cricket by their success in the county game. They certainly bowled with perseverance and discipline but, on this surface, they lacked the menace they have possessed elsewhere.

Perhaps unsurprisingly, Jack Leach was not at his best. Coming into this game, he had bowled only eight overs in first-class cricket since November and there was little assistance for him in the surface. While steady, there were more release balls - not least the full toss which Cook thumped through the covers to bring up his century - than he would have liked.

Most of all, though, there was Cook. In a season in which ball has dominated bat, he showed the old virtues of a straight bat, a calm mind and the patience to bat all day. It was the highest of his seven centuries at Lord's and, during the course of the innings, he surpassed Ricky Ponting and Steve Waugh's run tallies in first-class cricket. While long-form cricket remains, players like Cook will always be valuable.

With his captain, Tom Westley, Cook added 170 in 51.2 overs for the second wicket. While Westley struggled for fluency - only 15 of his runs came on the off side and his half-century occupied 128 balls - his highest innings of the campaign proved valuable for his team. At that stage, it seemed Essex may be able to establish a significant first-innings lead.

But when Westley flicked Tom Lammonby to midwicket straight after tea - Somerset had two men positioned for the stroke - Essex stuttered. Dan Lawrence, unsettled by a series of short balls from Gregory, mistimed a pull to midwicket and Paul Walter missed Gregory's very next ball, as Essex lost three for 11.

But Cook soldiered on. Now partnered by Ryan Ten Doeschate, he added another 56 for the fifth wicket and became the only man to reach 500 runs in the competition this season. Nobody has scored more than his two centuries, either.

In the dying moments of the day, though, the new ball accounted for the pair of them. Cook's wicket perhaps also owed something to the setting sun which appeared to be shining directly into his eyes as it set behind the pavilion. But he was making no excuses.

"Let's not blame the light," he said. "It was quite a good ball and I should have left it. But the sun is coming down and it is very awkward. But it's the same for both sides."

"Today was a real test," Gregory admitted. "The wicket was slow and Alastair showed his class. We couldn't get him early and he did what he's been doing for a long time now. He's been a fantastic player for a long time and he showed today why he's one of the best."