(CNN) -- Manchester United edged closer to a record 20th English Premier League title despite having to rely on a late equalizer from Robin van Persie to rescue a draw at West Ham.
The Dutch striker looked offside as he finished off from close range in a match that left both managers unhappy with the officials.
Manchester City's victory over lowly Wigan means they reduced the gap between themselves and United to 13 points but Alex Ferguson's side can still win the title as early as Monday if results go their way.
In Wednesday's other English top flight game Chelsea won 3-0 at local rivals Fulham to move back into third place in the table and edge ahead of London rivals Arsenal and Tottenham in the battle for the European Champions League places.
At Upton Park, Manchester United were put under pressure right from the start by West Ham, who took the lead after 16 when Ricardo Vaz Te nodded home after being set up by England striker Andy Carroll.
United leveled on the half hour mark when Japan international Shinji Kagawa teed up Antonio Valencia to slot home from close range.
Just before halftime, Carroll caught United goalkeeper David De Gea after going up for a corner -- a challenge that infuriated Ferguson, who later said it should have been a red card.
West Ham retook the lead ten minutes after the break as Mohamed Diame fired a low shot into the corner past De Gea.
But United rescued a point when van Persie tucked home from close range after Kagawa's effort had hit both posts, though replays showed he had been offside from the initial shot.
United can be confirmed as champions if they defeat Stoke on Monday night, but only if City lose to Tottenham the previous day.
Ferguson told Sky Sports: "We had to stand up to a lot, we kept going and twice came back. We had determination and courage to play. I was pleased with the result.
"They are very, very aggressive, you hope for a strong referee and I don't think we got that. We don't like losing and they showed that again tonight. Their goalkeeper saved them in the last 20 minutes."
His opposite number Sam Allardyce said: "The linesman's taken a famous victory away from us. To draw via a default goal from Manchester United is hard to swallow.
"They shouldn't make their mistakes. If players make those kind of mistakes they are dropped. Its a massive decision he's made. I'm bitterly disappointed."
City's victory came courtesy of a superb late winner from Argentina striker Carlos Tevez though they were made to live through some nervy moments by Wigan, who are battling relegation.
England goalkeeper Joe Hart had to save brilliantly from Wigan striker Franco Di Santo in the first half before Tevez beat two men and fired into the roof of the net in the 83rd minute.
"We were so tired. Wigan played good football, I think they will stay up. Carlos's goal was fantastic," City manager Roberto Mancini was quoted as saying by the Premier League.
Chelsea cruised to a 3-0 win over Fulham to strengthen their claim on a Champions League spot and move into third place.
Two goals from John Terry and a thunderous 35-yard strike from Brazil international settled the west London derby. Chelsea are a point ahead of Arsenal with a game in hand and three clear of Tottenham in fourth.
In Italy, Roma set up an Italian Cup final with city rivals Lazio after beating Inter Milan 5-3 on aggregate in their semifinal.
Leading 2-1 from the first leg Roma went 1-0 down early on but hit back with three goals, two from Mattia Destro and one from Vasilis Torosidis before Ricardo Alvarez grabbed a consolation for Inter.
The final, due to take place at the Stadio Olimpico ground both clubs share, could prove a headache for the authorities after last week's derby between Lazio and Roma was marred by violence, leading to eight arrests.
In Germany, Stuttgart set up a German Cup final with Bundesliga champions Bayern Munich after beating Freiburg 2-1 while Paris Sanit-Germain were knocked out of the French Cup by Evian.