The championship featured a dramatic battle between Senna and former teammate Alain Prost, who had made the switch to Ferrari.
Prost mounted Ferrari's first title challenge for several years, and led the championship after three consecutive mid-season wins.
Senna fought back strongly and went into the penultimate round at the Suzuka circuit in Japan with a nine-point lead over Prost.
The Brazilian Grand Prix was returned to the Interlagos Circuit for the first time since 1980, with a shorter track layout after a major renovation of the facility.
Unexpected rain in qualifying led to a grid with Gerhard Berger on pole position with Pierluigi Martini second in the Minardi, Andrea de Cesaris third in the Dallara, Jean Alesi fourth in the Tyrrell, Ayrton Senna down in fifth and Nelson Piquet sixth.
After that, Thierry Boutsen passed Piquet to take third with Stefano Modena's Brabham and Satoru Nakajima's Tyrrell getting the final points.
There was a six-week gap before the San Marino round, at the Autodromo Enzo e Dino Ferrari near Bologna in Italy; a number of changes were made to most of the cars during this period.
Patrese pulled away and won his first Grand Prix since South Africa in 1983 from Berger, Nannini, Prost, Piquet and Alesi.
At the front, Senna won from Alesi, Berger, Boutsen, Alex Caffi in the Arrows and Éric Bernard's Larrousse.
Canada was next and at the Circuit Gilles Villeneuve in Montreal the McLarens were 1–2 in qualifying with Senna ahead of Berger with Prost third, Nannini fourth, Piquet fifth and Boutsen sixth.
After Canada came the Autodromo Hermanos Rodriguez in Mexico City and Berger qualified on pole position with Patrese beside him and Senna third, Mansell fourth, Boutsen fifth and Alesi sixth.
Nannini moved into third but was then forced to retire with electrical trouble, while Prost finally passed Capelli with three laps to go.
Britain was next and Mansell, roared on by his home fans at the fast Silverstone airfield circuit, took pole from Senna, followed by Berger, Boutsen, Prost and Alesi.
Mansell remained second until lap 56 when his gearbox failed altogether; he promptly threw his gloves into the crowd and announced his retirement from Formula One at the end of the season.
At the start of the second half of the season, there was one change in pre-qualifying: Larrousse-Lola's five points meant that they were automatically promoted into main qualifying, dropping fellow French team Ligier into the Friday morning session.
At the historic Spa-Francorchamps circuit, McLaren were 1–2 with Senna on pole ahead of Berger, Prost, Boutsen, Mansell and Patrese.
However, Paolo Barilla crashed his Minardi heavily at Eau Rouge, sending debris all over the track and causing the race to be stopped again.
McLaren held a comfortable lead in the Constructors' Championship with 96 points against Ferrari's 63, with Williams third with 42, and Benetton fourth with 40.
After Belgium came Italy and at the historic Monza Autodrome near Milan, Senna took pole again with Prost second, Berger third, Mansell fourth, Alesi fifth and Boutsen sixth.
The top three then began to battle for the lead but none were able to close in on the other while Mansell continued to drop back, fighting a faulty throttle return spring.
In Portugal, at the Estoril circuit near Lisbon, the Ferraris took 1–2 in qualifying with Mansell ahead of Prost, Senna, Berger, Patrese and Piquet.
He pulled away fast but then hit Phillipe Alliot while lapping him, pushing the Ligier into a wall while Mansell got away with no damage.
Two laps later, Suzuki and Caffi collided and with the latter stuck in the cockpit in a zone with the wall next to the track, the race was stopped.
During a hot lap on the Friday, the Northern Irishman suffered a suspension failure on one of the fastest corners of the circuit, sending his Lotus into the barriers head-on.
The car was destroyed while Donnelly was thrown across the track with his seat still strapped to his back; he suffered severe leg fractures and bruising on his brain and lungs.
Senna, shaken by this incident, took his 50th career pole position ahead of Prost, Mansell, Alesi, Berger and Patrese.
Piquet, who had not pitted, held a narrow lead over Prost; the Frenchman pressured him into running wide on lap 29, dropping him down to fourth.
Similarly, McLaren retained a strong position in the Constructors' Championship with 118 points against Ferrari's 100, with Williams a distant third with 49, and Benetton fourth with 47.
However, Senna was unhappy at the pole being located on the dirty side of the track and thus the second place being on the racing line which should give the second-placed driver the advantage into the first corner.
On lap 2, Berger accidentally hit the engine kill switch allowing Mansell to get ahead before he could bump start the McLaren.