Verstappen's Red Bull team have taken the championship initiative by winning the past three races and lead Mercedes in the constructors' table by 37 points.
Here, the PA news agency looks at a battle which has lived up to its pre-season billing.
Why are Hamilton and Mercedes not getting it all their own way?
Hamilton's Mercedes team have won the past seven drivers' and constructors' championships following the most dominant period Formula One has ever witnessed, with the Briton marching to six of the last seven individual titles. But the grid's all-conquering team are in the midst of their sternest examination with Verstappen leading Red Bull's charge. Verstappen has long been earmarked as the heir to Hamilton's throne and now provided with a machine equal to, and probably better than Hamilton's Mercedes, the sport is enjoying one of its best seasons in recent memory with the two leading protagonists going wheel-to-wheel.
What's gone wrong at Mercedes?
Hamilton galloped to his record-equalling seventh world title with three rounds of last season's Covid-disturbed calendar to spare, and following only minor tweaks to the regulations (ahead of a major technical overhaul in 2022) the Briton was expected to dominate again. But a mandatory rule change to floors of the cars – introduced to reduce downforce – has hurt Mercedes more than others. Red Bull have also raised their game, and in Verstappen have a driver more than capable of ending Hamilton's stranglehold in the sport. It also does not help Hamilton that his team-mate Valtteri Bottas is a man shot of confidence and fighting to save his seat.
How alarming is the current state of play for Hamilton?
Very. The seven-time world champion drove brilliantly at the opening round in Bahrain and then in Spain and Portugal to beat Verstappen in a largely inferior machine. But his Mercedes car was desperately slow at the ensuing street circuits in Monaco and Azerbaijan, while they also struggled at Circuit Paul Ricard this weekend – hugely concerning given its a venue which has been so kind to them in recent seasons. Tactically, Mercedes were also all at sea in France, scuppering Hamilton's fine work and a chance of an unlikely victory, when they were too slow to react to Red Bull.
Can Hamilton turn it around?
Of course, it is premature to declare Hamilton's chances of winning a record eighth title over. He is still performing at an extremely high level and with 16 scheduled rounds remaining, the championship could yet swing back in his favour. But make no mistake, the momentum is with Red Bull and Verstappen. Chinks are beginning to show in Mercedes' armoury – one which has been resolute for so many years. Strategically they have not been good enough, team principal Toto Wolff has perhaps been ruffled by Red Bull counterpart Christian Horner's off-track barbs, while the row the legality of Red Bull's flexi rear wing has provided too much of a distraction. Red Bull only seem to be getting better, while Mercedes are heading in the other direction.