Arsene Wenger warned his young Arsenal side cannot continue to miss "major opportunities" like at West Ham if they are to go on to deliver the Barclays Premier League title.
The Gunners had looked in complete control at Upton Park yesterday following first-half goals from Robin van Persie and William Gallas.
However, Carlton Cole pulled a goal back when rookie Italian keeper Vito Mannone pushed a free-kick into the six-yard box, before substitute Alessandro Diamanti netted a late penalty after Alex Song was adjudged to have tripped the England striker.
West Ham finished with 10 men when Scott Parker was shown a second yellow card, but were not to be denied a much-needed positive result as England keeper Robert Green - somewhat at fault for the opener - produced a fine reaction save from van Persie's bullet header during stoppage time.
While the draw moved Arsenal up into third on goal difference above north London rivals Tottenham, whom they host next Saturday, a fifth straight league win would have capitalised more on Manchester United's defeat at Liverpool and closed the gap on leaders Chelsea to three points, with a match in hand.
"It is very frustrating," said Wenger.
"It is, of course, a major missed opportunity. In our job, you do not have this luxury.
"You need to get points when you deserve to get points and sometimes when you don't deserve to get the points.
"We never got them when we deserved them - and that means we have not made the maximum of what we should have done.
"But we have to keep the positives as we played well and are a strong team.
"We want to learn to finish these games off which is basically the most important lesson of the day.
"We have a great chance [for the title] this year, but you cannot repeat this kind of performance we had and not come out with three points."
While Wenger felt referee Chris Foy was somewhat "generous" with what proved the key decisions, the Arsenal manager called for his youngsters to be more clinical.
"We complicated our game a little bit and had five or six chances in the second half, but we missed the final ball," he said. "That is what we have to learn."
West Ham manager Gianfranco Zola praised the fighting spirit of his team.
The introduction of both Diamanti and England Under-21 international Zavon Hines helped inject fresh impetus to the Hammers frontline.
He said: "No matter what, the spirit has to be there all the time. That is something we can not do without.
"Last week [at Stoke] I saw something, a change and it is very important and against Arsenal, I have seen something more.
"It was very difficult to come back from that situation, but we did it and I am very pleased and proud of them."
While the Hammers - who have not won in the league since the opening day - remain in the bottom three, the Italian coach feels he has enough to be positive for the challenges ahead.
"With that spirit and with the qualities we have in the team, I think we can do better things," said the Italian.
"This team has got quality. We just need a bit more confidence."
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