An improved second half performance was not enough for Chelsea, as a stoppage time Fabio Carvalho goal prevented the Blues from coming away with all three points.
Enzo Maresca's men started poorly, failing to test Bees goalkeeper Caoimhin Kelleher and paid the price on 35 minutes when Kevin Schade capitalised on some lacklustre defending to slot home for 1-0.
However, a triple change at the break from Chelsea seemed to improve things, before the introduction of Cole Palmer made all the difference. Palmer, on his return from injury, fired home from close range just five minutes after coming on.
The West Londoners thought they had scored the winning goal with five minutes to go, when Moises Caicedo rifled the ball home on the edge of the area. However, deep into added time, a long throw-in from Brentford resulting in Carvalho sneaking in at the backpost to ensure the points were shared.
Here is how the Chelsea players rated against Brentford:
Starting XI
Robert Sanchez - 7
An impressive display between the sticks from Chelsea's number one, who made some vital saves in the second half. The Spaniard denied Kevin Schade at 1-1, before keeping out the Bees on a handful of occasions late in the day, but could do nothing to prevent the equaliser.
Wesley Fofana - 6
Despite being deployed as a right-back, the Frenchman put in a good shift in the first 45 minutes, but was understandable substituted at the break to bring on a more attacking full-back in Reece James.
Trevoh Chalobah - 6
The 26-year-old was Chelsea's best defender on the night, wasn't afraid to go in for challenges and played some good balls forward. However, he did lose the ball high up the pitch which resulted in Schade breaking the deadlock, leaving gaps at the back.
Tosin Adarabioyo - 5
The former Manchester City academy graduate failed to close down Schade for the opening Brentford goal and looked shaky at the back at times.
Jorrel Hato - 4
Starting in place of Marc Cucurella, it was a night to forget for the young Dutchman, who lost possession multiple times and struggled to get into the game. Was shown a yellow card for a bad foul on Igor Thiago which summed up his performance.
Moises Caicedo - 9
Another excellent performance in the middle of the park from the Ecuador international, who was composed and didn't put a foot wrong. Scored a stunning strike late on which would have been a perfect way to win the game, but it wasn't to be.
Enzo Fernandez - 7
Not the most standout performance from Fernandez but the midfielder still played his part nonetheless, delivering an excellent cross into the penalty area which resulted in Palmer levelling the game.
Pedro Neto - 6
The Portuguese winger grew into the game after a shaky start and caused problems down the right flank. Despite a chance to make it 2-1, he ultimately made very little impact on the game.
Facundo Buonanotte - 6
Chelsea's deadline day signing was a surprise inclusion to Maresca's starting eleven but managed to show signs of promise going forward. Was slightly unfortunate to have been taken off at the break.
Jamie Gittens - 5
A difficult display from the 21-year-old, who struggled to get the better of wing-back Michael Kayode and failed to make an impact. Was rightfully substituted in place of Palmer, which was seen as a much needed upgrade.
Joao Pedro - 6
The Brazilian struggled to test the goalkeeper and was frustrated against a stubborn Brentford defence. However, he still managed to contribute to the game by assisting Palmer for the equaliser.
Substitutes
Tyrique George - 5
The winger had a great chance to level the game just five minutes after coming on, drawing a good save from Kelleher but that was all the youngster was able to offer.
Reece James - 6
The Chelsea captain's introduction was very much needed as he assured things up at the back.
Marc Cucurella - 6
Not the most inspiring performance from the left-back but similarly to James, the Spaniard helped improve things defensively.
Cole Palmer - 8
Chelsea's starboy made the biggest impact off the bench, scoring just five minutes after coming on - his first Premier League goal from open play since January.
However, he missed a huge opportunity to score a second when he fired a close range shot straight at the goalkeeper, a chance he really should have put away. Nonetheless, it was certainly a welcoming return for the England international.
Alejandro Garnacho - 6
It proved to be a mixed debut from Garnacho, whose cross into the middle resulting in Caicedo scoring, but was at fault for the stoppage time Brentford goal having failed to mark Carvalho at the backpost.