Lampard, who took over as caretaker manager last week, has overseen two losses away at Wolverhampton Wanderers in the Premier League and at Real Madrid in the Champions League quarter-final first leg.
Brighton are seventh in the league, seven points ahead of 11th-placed Chelsea, and Lampard said there was no time to savour his return to Stamford Bridge where the club's all-time top scorer previously managed for 19 months between 2019-2021.
"I'm delighted to be back and the honour never falls short. I loved every minute and I'm happy to be back," Lampard told reporters ahead of Saturday's game.
"But the overriding feeling is focus on the job. I'll appreciate being back, but I'll have my serious face on."
However, Kalidou Koulibaly (31) will not be available after the centre back injured his hamstring against Real Madrid, with the defender set for a spell on the sidelines.
"No, he won't be available for either game... He won't be ready for weeks rather than days," Lampard said.
Lampard added Koulibaly's injury was more of a disappointment in the Champions League where they have named a different squad but added it was also an "opportunity" for others to step up.
Brighton are seeking European football for the first time in the club's history and Lampard praised their progress over the years but did not want to compare it with Chelsea's evolution under the new owners.
"I want people to understand this is a really tough game for us, falling in between the two Madrid matches. We will have to be some way towards our best and physically compete with Brighton," he said.
"Brighton is a fantastic model. You can track their last five or six years and see good progression from the Championship to the Premier League.
"Chelsea's path is a different one and we've been successful for a long time. There's now a transition between owners. When you're in a process, in a project, you'll have to dig in."
Lampard also said they would have to "manage" N'Golo Kante (32) after the Frenchman returned from a long injury layoff this month.
"When he's fit he's clearly one of the best midfielders in the world. He always offers massive output and quality," Lampard said.
