Valtteri Bottas says his disappointing Canadian GP has served as a "wake-up call" in his championship battle with Lewis Hamilton.
Mercedes are introducing their first engine upgrade of the 2019 season for this weekend's Canadian GP.
Mercedes will run with a special red-coloured halo over the Monaco GP, while Ferrari's Vettel is wearing a Lauda tribute helmet.
Valtteri Bottas set the pace for Mercedes from Ferrari's Charles Leclerc on the first of two days of F1 Testing at Barcelona.
Lewis Hamilton believes the start of Sunday's Spanish GP could prove "decisive" as he bids to turn the tables on Valterri Bottas.
Sky F1's Jenson Button hailed Valtteri Bottas' performance in Spanish GP qualifying, but believes Lewis Hamilton will retain confidence.
Mercedes have explained the issues which further complicated Lewis Hamilton's Barcelona qualifying amid Valtteri Bottas' flying form.
Valtteri Bottas has praised Mercedes' upgrade as a "good step forward" after enjoying a perfect start to his Spanish GP weekend.
Valtteri Bottas maintained his early advantage over Lewis Hamilton at the Spanish GP as Mercedes outpaced Ferrari again.
Lewis Hamilton admits a title battle with team-mate Valtteri Bottas will inevitably create tension, but isn't expecting conflict.
Sky F1's Damon Hill believes Valtteri Bottas has successfully raised his game against Lewis Hamilton and the title could be an exclusive duel.
Toto Wolff has stressed that Mercedes won't allow Lewis Hamilton and Valtteri Bottas' relationship to "deteriorate" like the Briton's did with Nico Rosberg.
Lewis Hamilton says he was "too friendly" to Valtteri Bottas at the start of the Azerbaijan GP and labelled his performance "under par".
Valtteri Bottas wrestled the lead of the F1 championship back from Lewis Hamilton after beating his team-mate to Azerbaijan GP victory.
Lewis Hamilton and Valtteri Bottas have played down Mercedes' undefeated start to F1 2019, stressing the car is not yet the easiest to drive.
F1's top two teams have each warned that the Chinese GP is far from settled yet with the prospect of a big battle on Sunday.
Mercedes still see themselves as the "challengers" in F1's title fight despite their commanding start to the season.
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Mercedes have revealed they discovered car damage on Lewis Hamilton's Silver Arrow after the world champion's defeat in the Australian GP.
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