United came from behind three times before the Mexican struck in the last minute to secure a 4-3 Old Trafford victory, moving Alex Ferguson's side seven points clear of rivals Manchester City who lost at Sunderland.
Manager Alex Ferguson labelled it a "championship winning performance" at the midway point of the season but Hernandez cautioned against complacency.
United led City by five points with four matches remaining last season but were pipped to the title by Roberto Mancini's side on a thrilling final day.
"It's a great position but we're not going to think we have already done the job," Hernandez told the club's website (www.manutd.com).
"This gap is going to give us a lot of confidence, but we want to just try to do the same in every game: win and get three points."
United host high-flying West Bromwich Albion at Old Trafford on Saturday (1500 GMT) but will be without key striker Wayne Rooney who has been ruled out of action for two or three weeks with a knee injury.
City travel to Norwich City (1500 GMT) looking to get back on track following a 1-0 defeat at Sunderland.
"We need to change something in our team because we can't continue like this - we score too few goals," said Mancini, who remains unfazed about the gap to United.
"Seven, six or four points, it doesn't matter the season is long. United concede a lot of goals but they score a lot so they have a chance but we can recover points."
Goalkeeper Joe Hart said City had the firepower required to make up the deficit.
"We've had leads, United have had the lead - it's to-ing and fro-ing at the moment," Hart told the club's website (www.mcfc.co.uk).
"We're a team of winners, it's hard and it hurts but we've got to move on. It is hard to lead and it is hard to chase too. We've clawed points back before, we proved it at the end of last year - we've just got to believe."
Lurking behind City are European champions Chelsea, who have a game in hand and play away at in-form Everton on Sunday (1330).
Chelsea have hit form under interim manager Rafael Benitez after following up their 8-0 demolition of Aston Villa by winning 1-0 at Norwich on Wednesday.
Tottenham Hotspur could move three points ahead of Everton and West Brom in the race for fourth when they travel to Sunderland on Saturday (1245).
Arsenal, currently seventh but also with a game in hand after their Boxing Day fixture against West Ham United was postponed on Dec. 19, take on Newcastle later on Saturday (1730).
Bottom club Queens Park Rangers host Liverpool on Sunday (1600) while Reading, also on 10 points but with a superior goal difference, welcome West Ham on Saturday (1500).
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