Ireland international Paul Shields was preferred to Hartley in the Saints line-up, but the replacement made an almost immediate impression after coming on in the 48th minute.

Hartley took a long pass from young scrum-half Lee Dickson and crashed through a tackle before stretching for the touchdown.

"You need a competitive squad and Paul Shields played really well in pre-season," said Mallender.

"We've said all along that those guys who play well will get rewarded with a start. You've got to have strength in depth."

A crowd of 13,094 saw Northampton enjoy a happy return to the Premiership following relegation to National Division One, but Mallender is taking nothing for granted ahead of the rest of the campaign.

"There's a lot of expectation and quite rightly so because it's a fantastic rugby-loving town," he said.

"I'm just delighted we could get off to a good start but we're certainly not going to get carried away because we know the next 21 games are going to be tough.

"We need to keep working at our set-piece, we were a little bit untidy in the line-out and at the base of the scrum so that's an area we need to improve.

"Whether the new laws affect that, who knows, probably yes."

Director of rugby Mallender also praised forwards coach Dorian West for his work helping adapt to the rule changes at the breakdown.

"Dorian did a fantastic job in that area," said Mallender.

"You've got to stay on your feet as much as possible and clear people out. You can't actually go to deck.

"We like it, we think it's fantastic that referees are refereeing in that way. We're fans of that."

Worcester boss Mike Ruddock will be examining that area closely after admitting he was "hugely frustrated" by his side's performance.

"We didn't really play," said Ruddock.

"Northampton pressured us in the lineout, poured through and made things difficult for us. In the tackle too, they put a lot of pressure on us.

"We gave away a lot of penalties and we need to look at that closely. Obviously I've got some concerns over the interpretation of the directive at the tackle area.

"But, in fairness, Saints deserved the victory."

Ruddock described the sin-binning of flanker Tom Wood just before Hartley's try as "significant".