Barcelona F1 test: Button leads first morning for McLaren

The McLaren driver, completing some aerodynamic evaluation for his team, elected to run Pirelli's softest tyres to set his best time of 1m23.753s a few hours in to the session, but Sebastian Vettel was only just behind him.

Vettel kicked off a key test for Ferrari to set the second fastest time, as the team focused on resolving its qualifying issues and getting to the bottom of what went wrong in Spain last weekend.

The German spent most of the morning on short runs and with the soft tyres that had been used at the Spanish GP to try to recreate the conditions that Ferrari had struggled with on Saturday.

During a run shortly before the lunch break, his best lap of 1m23.763 was just one hundredth of a second slower than Button managed.

Nico Rosberg was third fastest, having returned to action for Mercedes for the first time since his opening lap collision with Lewis Hamilton at the Spanish Grand Prix.

The German spent the morning running on medium tyres to set his best lap of 1m25.099s.

Williams caused the biggest stir of the morning when Alex Lynn began aerodynamic evaluation work for the team that involved some radical wing components. The British driver set the fourth quickest time of 1m26.071 in the process, before reverting to the more usual configuration

The double decker wing and sensors on the front of the car gave it a radical look, even though their dimensions are outside of what the regulations allow.

But in producing a downforce increase, it allowed the team to better understand car balance and what can be expected in 2017 when new rules kick in.

Daniel Ricciardo got his first taste of the upgraded Renault engine to set the fifth fastest time, ahead of Manor's Pascal Wehrlein and Renault reserve Esteban Ocon.

Day 1 morning results

Pos.	Driver	Team	Time	Gap	Laps
1	Jenson Button	McLaren	1:23.753		39
2	Sebastian Vettel	Ferrari	1:23.763	0.010	49
3	Nico Rosberg	Mercedes	1:25.099	1.346	54
4	Alex Lynn	Williams	1:26.071	2.318	41
5	Daniel Ricciardo	Red Bull	1:26.086	2.333	31
6	Pascal Wehrlein	Manor	1:26.464	2.711	50
7	Esteban Ocon	Renault	1:26.530	2.777	47
8	Romain Grosjean	Haas	1:26.669	2.916	35
9	Pierre Gasly	Toro Rosso	1:27.795	4.042	38
10	Alfonso Celis	Force India	1:28.570	4.817	34