The team-mates failed to win a race between them during the first nine rounds of the MotoGP season, with Honda's Marc Marquez dominating the first half of the competition by topping the podium every time.
Lorenzo - runner-up to Marquez last season - has only finished on the podium in three races, while the experienced Rossi has finished second four times but failed to convert those promising performances into maximum points.
The Italian signed a new two-year contract with the team in early July and Meregalli believes the 35-year-old and team-mate Lorenzo can turn the heat up on Marquez in the final nine races.
"We are happy [with Rossi]. The victory is still missing but we are working hard to get it as soon as possible," Meregalli told the MotoGP website.
"He started in the right way, since the Sepang 1 test, he really liked the changes that the Japanese engineers made during the winter time. He adapted himself to the new tyres and the new bike and he never gave up.
"He is always improving and pushing and that’s his attitude. His riding this year has been unbelievable and if he has signed it means he really believes he can keep pushing for two more years."
On Lorenzo, he added: "For me Jorge's capability was shown in the Mugello race [where Lorenzo finished 0.121 seconds behind Marquez].
"We are really expecting in the second part of the season to see him really strong. We are working really hard to make the circumstances suitable for him to be able to win."