Brentford defender John Egan scored twice just after the break to consign the Blues to a 2-0 defeat at Griffin Park. Egan nodded home a header on 48 and then slammed in a rebound eight minutes later.
Boss Mick McCarthy made two changes from the team which beat Barnsley 4-2 on the opening day. Hat-trick hero Grant Ward was handed his first league start for the Blues, as was loanee Conor Grant, the duo having come on as half-time subs last week.
The pair started in wide roles, Ward on the right and Grant on the left, with Freddie Sears moving up front alongside Daryl Murphy.
The injured David McGoldrick dropped out of the squad, while Teddy Bishop moved to the bench. New re-signing Luke Varney wasn’t included in the 18.
Ward struck the first shot of the game in the third minute after Ryan Woods needlessly surrendered possession midway inside his own half. The 21-year-old brought the ball forward before hitting a powerful low drive which Brentford keeper Daniel Bentley claimed confidently.
Neither side created another opportunity in the first quarter of a hour in a fairly open and even game but with little penalty area action.
On-loan Everton man Grant went close to his first Town goal in the 17th minute when he curled a 25-yard freekick just past Bentley’s right post, Jonas Knudsen having been fouled.
Grant went close again in the 21st minute after breaking into the area on the left having been fed by Murphy but Bentley managed to bundle his low near-post shot wide. From the resultant corner Christophe Berra headed over.
Town continued to look the more dangerous side and almost went in front in the 24th minute.
Sears fed Knudsen to his left and the full-back sent over a low ball to Ward, whose effort was blocked by Callum Elder. The ball cannoned off Sears to Murphy at a tight angle on the right but the Irishman was only able to turn on to the roof of the net.
Brentford’s first chance of the game came in the 32nd minute when Woods threaded in Josh Clarke between Berra and Knudsen. But, with the Danish international putting him under pressure, Clarke screwed his shot well wide.
Adam Webster picked up the game’s first booking for a foul on Scott Hogan in the 39th minute.
The Blues threatened again four minutes before the break when Cole Skuse played Murphy in on the left, however, the Irishman’s low ball towards Sears was cut out by Harlee Dean.
Brentford’s best chance of the half came a minute later, Webster challenged Hogan on the edge of the box and the ball fell to Lewis Macleod, who scraped a shot only just past Bartosz Bialkowski’s right post when he should have hit the target.
Soon after at the other end, Murphy flicked on a long ball to Sears on the edge of the box but the Town number 20, without a goal in 28 games, shot well wide.
That was the last chance of a half in which the Blues had had the better of the chances and Bentley was the busier keeper.
However, the Bees had started to look more threatening towards the end when Macleod should have done much better with his opportunity.
The second half was only three minutes old when the home side took the lead. After Webster had headed a cross from the right behind ahead of Bialkowski, Macleod sent over the corner and completely unmarked home debutant John Egan - he had escaped the attention of Webster - headed into the corner of the net with Bialkowski having no chance.
Brentford went looking for a second and on 52 Bialkowski did well to save from Macleod from a tight angle on the left. The Bees kept up the pressure and Knudsen did well to block a subsequent strike from Nico Yannaris.
The home side doubled their lead in the 56th minute when, after another corner on the right, Sears half-cleared to Yannaris, who hit a powerful low strike which Bialkowski couldn’t hold onto and Egan followed up to claim his second of the afternoon.
Town sought to get back into a game and on 58 Berra headed wide from a Grant corner after Bentley had come and failed to claim. Soon after, Ward volleyed a Knudsen cross from the left just wide.
Brentford threatened to make it 3-0 just after the hour when Romaine Sawyers was twice thwarted by the Town defence, Webster diverting his second effort behind.
Blues boss McCarthy switched Grant for Bishop in the 66th minute, then a minute later Brentford swapped Maxime Colin for Sam Saunders.
Soon after the substitutions Bialkowski tipped a powerful Macleod strike over with the Bees looking more likely to score a third than Town were to pull one back.
However, on 72 Bishop completed a one-two with Sears and whipped over a cross from the right which Murphy only just failed to reach at the far post.
There was another scare for the Blues a minute later when Bialkowski was forced to kick under pressure and only found Macleod but the former Rangers man looped back into the keeper’s hands.
Former Bee Jonathan Douglas replaced Bru on 78, initially to boos from the home fans which were quickly replaced by applause.
The substitute almost pulled a goal back two minutes after coming on. Following a freekick, he did well to find himself space before eventually scuffing to the keeper.
Brentford sub Saunders will feel he should have made it 3-0 in the 83rd minute when found by Sawyers’s cross from the right but he volleyed well over.
Moments later, Murphy was found at a tight angle at the far post and shot well wide when he probably should have played the ball across the area.
Two minutes later, with the Bees well on top and passing the ball around slickly, Woods curled just wide, then hit a subsequent effort past the same post.
A frustrated Murphy shot wide from distance on 88 before the Bees replaced Macleod with Konstantin Kershbaumer, then Josh McEachran came on for Yennaris as the game moved into injury time.
In the corresponding fixture on the opening day of last season the Blues were 2-0 up and Brentford hit back twice in injury time to level, but such a comeback never looked on the cards and referee Stephen Martin’s whistle confirmed Town’s first defeat at Griffin Park since November 1955.
Town had the better of the first half, although there were signs that the Bees were becoming more dangerous close to the break.
Egan’s two goals soon after the break took the game away from Town and they never really recovered and the Bees looked more likely to extend their lead than the tame Blues were to get back into the match.
Town have another tough away trip to Wolves on Tuesday before next Sunday’s East Anglian derby against Norwich City at Portman Road.
Town: Bialkowski, Chambers (c), Webster, Berra, Knudsen, Skuse, Bru (Douglas 78), Ward, Grant (Bishop 66), Sears, Murphy. Unused: Gerken, T Smith, Emmanuel, Kenlock, Dozzell.
Brentford: Bentley, Colin (Saunders 67), Elder, Dean, Egan, Yennaris (McEachran 90), Woods, Clarke, Macleod (Kershbaumer 90), Hogan, Sawyers. Unused: Bonham, Bjelland, Hofmann, Ledesma. Referee: Stephen Martin (Staffordshire).