Mercedes boss Toto Wolff says that despite the German outfit's lead in both F1 championships, it "doesn't feel" like it has an edge over its rivals.
Mercedes returns to actions this weekend at Spa with a comfortable 150-point lead in the Constructors' standings, while Lewis Hamilton's cushion over Silver Arrows teammate Valtteri Bottas in the drivers' standings is 62 points.
Both team and driver appear on paper to be well on course to secure their sixth title in their respective championships.
But Red Bull and Max Verstappen's increasing momentum, as reflected by the pair's wins in Austria and Germany, is keeping Mercedes on its toes and in alert mode.
"We're leading in both championships, but it doesn't feel that way," said Wolff ahead of this weekend's Belgian Grand Prix.
"In the last few years, we saw teams perform very strongly after summer shutdown, so we know we need to keep pushing.
"In that respect, we're approaching the start to the second half of 2019 more like the start to a completely new season - once again we need to make sure that we leave no room for error and keep raising the bar."
Wolff revealed is Mercedes' preview that while its Brackley factory was idled during the summer break, there was no letting up down the road at its Brixton power unit base.
"While the majority of our colleagues in Brackley had the chance to recharge their batteries for the second half of the season, other team members were carrying the baton over the past weeks," he said.
"Our team members in Brixworth worked straight through the F1 summer break to improve the performance and reliability of our Power Unit.
"It's great to come back from the summer break knowing that part of the team was still pushing flat out, and we are grateful to our colleagues who kept the ball rolling while we were out of office."
Spa's power-circuit characteristics will hopefully open up the battle at the front, with Ferrari expected to give Mercedes a run for its money around the legendary Ardennes circuit.
"Finding the right set-up is tricky because the track has a challenging mix of long straights, a wide range of corner speeds and also considerable elevation changes," conceded Wolff.
"The weather can also be somewhat unpredictable in the Ardennes which can make the sessions very interesting. We're looking forward to the fight."