Barcelona - Lewis Hamilton fired a warning for his team-mate on Friday when, after being outpaced in both practice sessions at the Spanish Grand Prix, he revealed that his performance engineer has been switched to work with Mercedes team-mate Valtteri Bottas.
"That's been a nice helping hand for him - and he has learned a lot from that," said the defending five-time world champion of Riccardo Musconi's move across the Mercedes garage.
"The things I was doing with my settings - which my former engineer is now encouraging him to do - has definitely helped him move in the right direction. So, the little step he has taken is to be expected.
"I now have a new engineer. We work well together, but it takes time to build a relationship. It is not as strong as something that has been built over six years."
Hamilton's explanation for Bottas's new surge of pace and progress to leading the early-season drivers' championship came after a day in which the Finn shone and topped the times in both sessions.
Musconi was promoted to become Bottas's race engineer after his predecessor Tony Ross moved to a position with Mercedes Formula E team.
His arrival has coincided with a dramatic upturn in Bottas's form, two wins in four races and the leadership of the title race ahead of Hamilton, who was just five-hundredths of a second slower in Friday's second practice as the two Silver Arrows men duelled for supremacy.
Ferrari's Charles Leclerc and Sebastian Vettel were a second adrift in third and fourth ahead of Max Verstappen in his Red Bull.
Hamilton's comments followed his pre-race praise for the team's code of conduct for the two drivers, a move made by Mercedes to avoid any repeat of 2016 when Nico Rosberg beat Hamilton to the title after a season of acrimonious incidents, including a first lap collision at the Spanish Grand Prix.
It confirmed also that tensions exist within Mercedes as the pair emerge as the most likely early protagonists in a title duel, unless Ferrari can quickly regain the pace needed to mount a serious challenge.
"Winning the championship is not just about winning a couple of races," said Hamilton, in another remark loaded with intent.
"It is about the whole season. It will be interesting to see how he goes in the harder conditions. We've only had four races so watch this space."
Hamilton also made plain his response to suggestions that this season could see him facing a similar scenario to that of 2016.
"I have grown a lot since then. I am much stronger in and out of the car and much better at knowing how to manage my relationships," he said, dismissing any thought of a breakdown in relations with the mild-mannered Bottas.
"I don't have any doubt in my ability. I am down for whatever challenge and whoever is going to challenge me. Everything is great within the team. The respect is there, so don't expect what you have seen in the past."
After a winless struggle in 2018, Bottas has relished the challenge of competing with Hamilton this year and continued to show his speed and vim with another strong showing on a warm, windy and dry day at the Circuit de Catalunya.
"It's always an interesting day when you bring new parts for the car to get a feel for it and see if they deliver the performance," he said. "Today, the car felt really good.
"It was completely different to how it was in winter testing and it seems like our cornering performance has improved. The balance around the lap is also better, so it looks like we've taken the right direction since the winter."
Max Verstappen was fifth for Red Bull, complete with their own upgrades, ahead of Romain Grosjean of Haas, Pierre Gasly in the second Red Bull and Dane Kevin Magnussen in the second Haas.
"We are happy, engine-wise," said Vettel, unfussed at trailing Mercedes again.
"Obviously, it's Friday so it's difficult to know what we are doing compared to the others yet. Car-wise we put everything on the car that we expected and I think it's fair (to say) that we haven't been the quickest."