Verstappen was left offline and with a tight entry into Turn Four, allowing Sergio Perez to sweep around the outside but contact with the right front of the Red Bull put the Racing Point around and down the order into last place.
Up ahead Hamilton’s tyres were far from optimal temperature and a lock-up into the Turn Five hairpin gave Bottas a sniff of the lead.
As raindrops appeared on the camera lenses, Bottas carried the confidence versus his team-mate and snuck his W11 into the lead at Turn Eight.
A lightning-quick start from Carlos Sainz put him into P3 following Verstappen and Perez’s contact, and into the blind Turn 11 dipped to the inside and snatched second from the pole-sitter.
As drivers fired up tyres, a more normal order began to emerge, with Bottas using DRS to nail Sainz for the lead on lap six and team-mate Hamilton following on lap seven to restore the Mercedes one-two.
Following his poor start, Verstappen had cleared Norris and Sainz by the opening of lap eight and set off in pursuit of Hamilton ahead. Bottas’ lead was up to two seconds and the raindrops were moving away from the Portimao circuit.
McLaren’s opening surge began to wane as the softer compound tyres fell away. Leclerc made light work of Norris with DRS assistance for P5, while Daniel Ricciardo dispatched Räikkönen with the powerful reduction in drag.
Verstappen radioed in on lap 10 that he was already feeling his front soft tyres going away as the sun emerged from the grey skies. Meanwhile, the Ferraris were on the move, with Sebastian Vettel up to P13 on his mediums while Leclerc cleared Sainz for fourth by lap 12.
As Verstappen slipped away, the two Mercedes flew into a 10sec lead, the gap stable at around 2sec between race leader Bottas and Hamilton. A string of fastest laps by Hamilton, beginning on lap 16, gradually began to close that gap to well within DRS range.
Lance Stroll was locked in battle with Norris for P6 and, in an incident similar to the Canadian’s practice contact with Verstappen, made contact with the McLaren on the inside of the first corner attempting to sweep around the outside. The contact sent the Racing Point into a spin and left both needing to pit with front wing damage.
Norris and Stroll rejoined from their stops in P19 and P20 respectively, with Ricciardo, Räikkonen and Alex Albon in front having already made the switch onto medium tyres. For the ambitious move on Norris, Stroll was handed a five-second penalty for the contact, further ruining Racing Point’s afternoon.
The pressure from Hamilton told on lap 20, with a DRS pass giving Hamilton the lead of the race before Turn One. The new leader wasted no time in stretching his advantage, surging into a 3sec lead by lap 23 despite reporting his front left medium tyre had started fading.
The early worries for Hamilton had clearly subsided by the halfway point. His pace was comfortably fastest of all, with a number of fastest laps to move 8sec clear. Engineer Pete Bonnington confirmed the Mercedes would be stretching the first stint as far as possible.
The FIA had altered track limit rules following the 100+ infringements during Friday practice, but that didn’t stop Stroll from becoming the first driver to pick up a five-second penalty for excursions outside of the painted kerbs to add to his other earlier sanction.
Sainz’s stop had put him outside of the top 10 and the McLaren came up against a resurgent Räikkönen for 10th place. The Spaniard attempted a brave move into Turn One around the outside that luckily didn’t end in contact. Sainz made the pass stick with DRS a lap later, but not before the Finn made him fight for it side-by-side for several corners.
One lap later and it was Perez and Esteban Ocon’s turn to go side-by-side in a battle lasting half a lap wheel-to-wheel. A series of switchbacks from Turn Three to Eight and the Mexican got the better of the Renault man for P5 in his fightback from the first lap contact with Verstappen.
Leclerc finally bolted on a set of hard tyres for his sole stop of the race on lap 35, rejoining fourth and 10sec down on the leading Red Bull driver.