The conventional wisdom about Arsenal’s title push is that they have the easy run-in. Compared to Chelsea and Manchester United it is apparently a piece of cake. A home game against the team above the relegation zone by virtue of goal difference was supposed to be one of the tastiest of the lot, but Arsène Wenger’s team came oh-so-close to suffering a terrible dose of indigestion.

The game hinged on a critical incident a minute before half-time, when Thomas Vermaelen was shown a red card for tangling with Guillermo Franco. Not so easy all of a sudden. But the way Arsenal regrouped, resettled, and finished off West Ham showed they have the heart to take this adventure as far as they possibly can. Their title rivals may have games in hand, but Arsenal wake up this morning looking down on everyone.

The quest now moves to Birmingham. For different reasons recent games have all felt central to the plot of this unfolding drama, but St Andrew’s is a challenge that feels particularly pivotal in terms of Premier League aspirations. Against the kind of direct opponents they have been known to find unsettling, they will travel without their first-choice centre-halves. As a prelude to Barcelona, its importance cannot be overlooked.

As much as it was natural for Arsenal to be thankful for the return of their captain and top scorer Cesc Fábregas, the reinstatement of Alex Song after a two-match suspension was equally reassuring. The Cameroonian anchor has been crucial, and has matured into an important safety net in front of a back line with a tendency towards fragility.

Alongside him Denílson was chosen ahead of Abou Diaby. This was surprising. A more creative player is the norm alongside Fábregas and Song in midfield, but Denílson was favoured ahead of Diaby and Tomas Rosicky. Was this an experiment with Barcelona in mind?

Arsène Wenger was firm that West Ham was the absolute priority, and the Denílson selection turned out to be an inspired one. The Brazilian provided his team with the gift of an early goal. He was alert to the opportunity to pickpocket Valon Behrami and skillfully smuggled the ball to Nicklas Bendtner. When it was returned to him, Denílson drilled a first-time shot into the bottom corner.

Denílson has elicited his fair share of moans from the crowd this season, especially during a period when he found the going tough in midwinter. But here he sparked. Maybe he had borrowed some of Bendtner’s enormous supply of confidence (there is plenty to spare). This was his fourth league goal from 16 starts this season, and not for the first time it was an important goal, too.

He might have had another soon after. At the end of a tippy-tappy move, Denílson chested the ball down and volleyed goalwards. His flourishes were all the more valuable as Arsenal were not at their fluent best in the first half. Fábregas took an early kick on the foot and looked very unhappy with the perpetrator, Behrami, with whom he later had words. The Catalan was not running freely at all and strained to exert any great influence. Samir Nasri and Andrey Arshavin were a little flat, too.

West Ham had enough glimmers to suggest Arsenal would be foolish to take this at too much of a presumptuous stroll. Junior Stanislas broke down the right flank and whipped in an inviting cross which Mido couldn’t reach, then Gaël Clichy and Sol Campbell made excellent interceptions as West Ham built towards goal.

In the last minute of the half, the pendulum swung viciously. Franco surged onto a high pass and Vermaelen missed the header, then in his desperation to retrieve the situation was clumsy as he tussled with the Mexican. Although contact was minimal, Franco tumbled inside the penalty area. The referee Martin Atkinson was so far behind the play he was closer to the centre circle than the penalty box, but trusted the instincts of his linesman. Not only did he point to the spot, he sent off Vermaelen. Wenger was infuriated, and waited at half-time to remonstrate with the officials.

In the meantime, Diamanti struck his kick well, but Manuel Almunia plunged to produce an inspired save. His record with penalties is one of his best features, and Arsenal were immensely grateful.

Interestingly, Wenger chose not to make a substitution and Song dropped back to fill in at centre-half. He had his work cut out as West Ham set about the second half with attack in their hearts. It was not long before Arsenal did make a change, with Diaby replacing Bendtner and Arshavin leading the line.

Arsenal hauled themselves back again to force the game up towards the edge of Rob Green’s box. Emmanuel Eboué became increasingly influential, and his ability to win free-kicks kept up the pressure. Campbell ambled up for a corner but headed too close to the keeper.

Gianfranco Zola, so desperate for points, sent on the attacking power of Carlton Cole and experience of Benni McCarthy. With 12 minutes to go a sizzling left-footer from Cole shuddered against the base of Almunia’s far post.

Back came Arsenal, and Matthew Upson handled in the box inexplicably as Fábregas bore into the danger zone. Another penalty. In the swirling rain, the captain steeped up to rifle in, Green diving the wrong way. “We are top of the league,” sang the crowd giddily. It ain’t easy, but it sure is scintillating.

ArsenalWest Ham UnitedPremier LeagueAmy Lawrenceguardian.co.uk

The main reason West Ham remain one point above the relegation zone is that they are blunter than a bad diplomat. Gianfranco Zola’s team offer plenty of elegant interplay but their lack of a cutting edge means they seldom score enough goals to win matches. In an effort to sharpen his side and ensure their survival, the manager has turned to an inconsistent 32-year-old, Benni McCarthy.

West Ham and Blackburn have agreed a transfer – whether it is a full-time move, as all parties want, or a loan depends on the type of work permit the Home Office issues. That will be made known today. Either way, next weekend Zola expects to deploy the South African alongside his top scorer, Carlton Cole, who, after two substitute appearances in the last week following a two-month absence for knee surgery, should be fit to start.

The West Ham manager believes the pair could be deadly, even suggesting they could be comparable to the Dwight Yorke-Andy Cole double-act that was once so successful for Manchester United. “There are similarities [to Yorke and Cole],” said Zola. “Carlton is strong and skilful and Benni is smart and skilful, so it will be a good combination. Sometimes it doesn’t take much time for partners to gel. I’ve seen partnerships develop straight away, where it just clicks, and I don’t think it will take them long. They will be a big asset for us.”

Next week West Ham play Burnley, who coincidentally were their opponents the last time Cole started a match, on 28 November. West Ham scored five goals that day, which is all they have mustered in the nine league games since. Against Blackburn the England striker came on in the second half and, in the 84th minute, had an opportunity to score what would probably have been the winning goal, only to wince in frustration as he misread the intention of Scott Parker, who, after skipping past two defenders, teed up a tap-in by rolling the ball across the face of goal. “I pulled back for him to play it into me and he’s gone across goal and it was gaping,” said Cole. “I felt reallybad that I wasn’t there.” Henceforth Cole will not be the only West Ham player trying to get on the end of passes in the box. “Benni will take a lot of pressure off Carlton for goals,” Zola said. “It will give him an opportunity to be more relaxed. Also, the opposition will no longer have to look after only one player but two.”

Blackburn could also have done with an in-form McCarthy at Upton Park, where Gaël Givet had a shot cleared off the line – by Cole, who at least proved decisive at one end of the pitch – and Jason Roberts failed to beat Rob Green after creating space for a shot 15 yards out. But McCarthy has rarely been on form for Blackburn over the last two years and he has not found favour with Sam Allardyce, who has suggested that he is a fading force. “West Ham are getting a hugely talented player but the overall situation is he’s not getting any younger so the legs aren’t quite as good,” said Allardyce. “If you can get other players around him to do the work, then he’ll use his talent to get chances and score you goals.” That is all West Ham want for now.

Premier LeagueWest Ham UnitedBlackburn RoversPaul Doyleguardian.co.uk