In the latest Talking Reds column, Kate Cohen looks at Lucas Leiva's influence on Sunday's crucial 2-1 win at West Ham United.

As Liverpool entered the half-time break level with West Ham, many fans (myself included) turned to social media or the person nearest them at the pub to vent their discontent with the referee's first-half decisions.

At the same time, Brendan Rodgers was plotting how his side would return to Merseyside with a vital three points before a top-of-the-table clash with Manchester City.

The decision to introduce Lucas Leiva and switch from a 4-3-3 to a 4-4-2 diamond was made, and what a brilliant decision it proved to be.

As the ball fell to him in the final third, within the blink of an eye Lucas had played a perfectly-weighted, defence-splitting pass. Bisecting West Ham's centre-back and right-back, out of reach of the retreating Mohamed Diame but tempting enough to draw out Adrian in goal, Jon Flanagan was brought down in the box. One touch to control, a quick glance, pass and penalty.

Steven Gerrard, who converted his second spot-kick of the match to secure the win, singled out Lucas' involvement for the goal.

"The ball he [Lucas] played for the second goal; people have been raving about Coutinho all year and the passes he's made but for me that was right up there with Brazil's best and that helped us to go on and get the win," he said post-match. Deserved praise for Lucas' performance.

But Lucas' influence was not limited to his involvement in the decisive penalty. Coming on at half-time he facilitated Liverpool's ability to carry out Rodgers' interval instructions - "I didn't think it was quite working for us [in the first half] and we couldn't dominate the game as much as I would have liked. We went to a diamond in the second half to give us numbers in the middle of the field and put the two strikers closer together, which could stretch them a bit more."

Whilst Liverpool saw the majority of possession in the first half (55.6 per cent), West Ham's high intensity, 'up and at 'em' game style did not allow them to actually control the ball to any real degree and to create goalscoring opportunities in the final third.

That changed in the second half. With Lucas, a calm distributor of the ball, as the extra man in midfield, Liverpool were able to completely dominate possession with 71.5 per cent. Lucas was able to complete 43 of his 49 passes, one of which was the decisive pass for the penalty. He was able to see considerably more of the ball than Philippe Coutinho, the man he replaced at half-time, who was only able to complete 22 of his 30 passes.

Lucas' passing chalkboard v West Ham, via Opta Stats 

With West Ham's tendency to attack down the flanks and cross the ball into the box, Lucas also needed to defend well in the 'diamond' formation. The narrow formation with four central players in midfield required Lucas, and Jordan Henderson on the other side of the 'diamond', to shuttle across to help out the full-backs. That energy in midfield allowed Liverpool to limit West Ham's main threat, regain possession and control the ball again.

The win saw Liverpool overcome a major challenge. Whilst it was far from their stand-out performance of what has so far been a remarkable season, Brendan Rodgers made a crucial half-time change to allow Liverpool more control of the match and that control was enough for Liverpool to see out the win and return to the top of the league. 

Follow the author @kate_lfc_sfc.