Hernandez has shouldered the goalscoring responsibility in the last two games to give United supporters something to cheer about after the trauma of last week's Wayne Rooney saga.
Hernandez, nicknamed 'Chicharito' which means 'Little Pea', scored twice at Stoke on Sunday and was hailed by United boss Sir Alex Ferguson after hitting an excellent winner in last night's 3-2 Carling Cup win over Wolves.
However Owen, who has just suffered another injury setback with a hamstring problem that will keep him out of action for several weeks, knows it only takes one bad performance to find yourself out of the team.
He told BBC Radio Five: "It's obviously early days for him but he's made a really good impression at the club, scored goals in the last couple of games.
"He's young, sharp and a good finisher. He seems to be thriving, he's always got a smile on his face, he enjoys his football and the fans have taken to him already.
"So far so good, but, as I know, football changes in a week or whatever.
"Hopefully it's the start of something good for him, but he needs to keep working hard and keep putting in those performances because at Man United that's what it demands - you score one week, but if you play poorly the next week then you could be out the team so you need to always be on top of your game.
"Thankfully he's playing well at the minute, and long may that continue."
Ferguson signed Hernandez for £7million from Guadalajara before the World Cup - an astute move as he went on to score two goals - including a brilliant one against Argentina - and to generally impress.
He has already impressed Wolves manager Mick McCarthy, who thinks he is going to be star.
McCarthy said: "I watched him at Stoke on Sunday and forget his goals, his all-round performance was terrific.
"Sir Alex knows what he's doing and he wanted to get the winner against us so he brought him on and that's what he did."
Meanwhile, Owen insisted the Rooney saga that caused such uncertainty over the striker's future had not affected United.
He added: "Everyone seems to be happy now. The club have got a world-class player signed for five years and obviously Wayne's happy and the manager's happy.
"Wayne is obviously ambitious and the club's ambitious. He wouldn't have signed if he had any doubts.
"Cutting out all the rubbish, the main thing is that he's signed.
"It's better having Wayne Rooney in your squad than not, so we're all happy in that way."