Match ends, Croatia 2, Wales 1.
A late Wales revival in Croatia proved in vain as Ryan Giggs' side suffered a setback in their bid to reach Euro 2020.
The hosts, who have never lost at home in European Championship qualifying, took the lead in the searing Osijek heat as James Lawrence turned Ivan Perisic's powerful, low cross into his own net.
Wales threatened to level but always looked vulnerable at the back and one episode of particularly calamitous defending early in the second half allowed Perisic to score the World Cup finalists' second goal.
Gareth Bale fanned the flames of a Welsh comeback with a handful of well-struck shots, and those faint hopes looked more like genuine belief when substitute David Brooks scored from 20 yards via a deflection.
But despite their late efforts in severely draining conditions - with a stretching Brooks agonisingly close to scoring a second - Wales fell short of snatching what would have been a valuable point.
Having beaten Slovakia in their opening fixture in March, Wales are now third in Group E, three points behind leaders and top seeds Croatia.
On Tuesday Giggs' men visit Hungary, who are away against Azerbaijan in the group's late kick-off on Saturday.
Wounded Croatia expose Wales
This was Giggs' 12th match in charge of his country and undoubtedly his toughest to date.
Croatia's unbeaten run at home in Euro qualifiers now stands at 32, a sequence that started with their first in 1994 - and they had not lost a home fixture of any sort since 2013, a run of 23 games.
Yet since reaching last year's World Cup final, Zlatko Dalic's side had endured a chastening Nations League campaign - humiliated 6-0 by Spain and beaten by England - before losing unexpectedly to Hungary in their second Euro 2020 qualifier.
Following those failures, Croatia were under pressure to win against Wales and they were quick to seize control as the temperature soared towards 30C.
Their captain and Ballon d'Or winner Luka Modric was typically composed and, with Mateo Kovacic and Marcelo Brozovic, formed a formidable midfield triumvirate.
As much as the hosts bossed possession, there were openings for Wales but two precious first-half chances were squandered by Harry Wilson and Will Vaulks.
The risk Wales took by attacking was to leave their defence exposed, with Perisic regularly finding himself in space on Croatia's left.
He had a handful of efforts on goal before forcing Croatia's opener and, even after that, Wales did not heed the warning.
Moments after a narrow escape when the hosts had a goal disallowed for offside, Wales' abject failure to clear their lines presented Perisic with a chance at the back post he gleefully accepted by rifling the ball past Wayne Hennessey.
Wales were in danger of a severe beating at this point but they were lifted by Brooks' introduction, with the Bournemouth youngster turning neatly to create the space for his shot which found the net thanks to a deflection from Domagoj Vida.
The Croatia centre-back was one of five home players to be booked, evidence of how Dalic's side were troubled by their opponents even as they monopolised possession for long periods.
This was more than a scare for the World Cup runners-up but, while Wales may take heart from their late rally, they may reflect on this game as an opportunity wasted because of their slipshod defending.
Giggs' work in progress
Wales are a work in progress under Giggs, a young side with rich attacking promise but occasionally naive and vulnerable defensively.
Those frailties were laid bare by Croatia's opening goal, as Modric's long ball found Perisic with an alarming amount of space on the left after Connor Roberts had broken forward with nobody covering for him at right-back.
Hennessey might have closed down Perisic but his hesitation gave the Inter Milan player enough time to drill a dangerous cross across goal, where Lawrence had little chance of doing anything other than scoring an own goal.
Croatia's second made for even worse viewing from a Welsh perspective, as several players failed to deal with a loose ball in the penalty area before it finally made its way to Perisic at the back post.
The positive for Wales is that, at this point when they looked set to capitulate, they actually improved.
Bale, whose influence has waned in recent games, brushed off Croatia's ugly attempts to kick him out of the game and attacked with purpose in the second half.
Brooks added to his burgeoning reputation with a bright display from the bench, while Joe Allen and his midfield colleagues Matt Smith and Vaulks battled valiantly against their impressive opponents in the exhausting heat.
But for all those notes of encouragement, there was a foreboding familiarity to the way in which Giggs' side contributed to their own downfall with their defensive mistakes.
There may still be a bright future for this young group of players but there are some worrying trends forming under Giggs, which the former Wales captain will need to address if he is to guide his nation to only a third major tournament in its history.
Man of the match - Ivan Perisic
A player of his standing should not be given so much time and space, and the Inter player punished Wales with a goal, an assist and a menacing all-round attacking display.
Match stats - Wales have never beaten Croatia
- Wales have failed to win any of their five games against Croatia (D1 L4), losing the last four and conceding twice in each of those defeats.
- Croatia have won their last four home matches since drawing 0-0 with England in the Nations League in October 2018.
- Wales have lost four of their last five away matches - winning the other one - as many as they had lost in their previous 14 (W5 D5 L4).
- Jamie Lawrence is the first player to score an own goal for Wales since Ashley Williams against Iceland in March 2014, five years and 95 days ago.
- Since the start of 2018, Ivan Perisic has scored more goals for Croatia (six) than any other player. However this was his first goal for his country in seven matches since September.
- David Brooks' strike was his first goal for Wales in his 11th appearance. He is the first player to score as a substitute for Wales since Ben Woodburn against Austria in September 2017.
- 16JedvajBooked at 50mins
- 6LovrenBooked at 54mins
- 21VidaBooked at 69mins
- 11BrozovicBooked at 90mins
- 7BrekaloBooked at 28minsSubstituted forPasalicat 66'minutes
- 8KovacicSubstituted forBadeljat 76'minutes
- 4PerisicSubstituted forSkoricat 90+3'minutes
- 12L Kalinic
- 23VaulksSubstituted forAmpaduat 66'minutes
- 8SmithSubstituted forBrooksat 65'minutes
- 11BaleBooked at 48mins
- 20JamesSubstituted forMatondoat 79'minutes
- István Kovács
- Shots on Target
Second Half ends, Croatia 2, Wales 1.
Foul by Mile Skoric (Croatia).
Ethan Ampadu (Wales) wins a free kick in the defensive half.
Attempt blocked. Mario Pasalic (Croatia) left footed shot from outside the box is blocked. Assisted by Mile Skoric.
Delay over. They are ready to continue.
Substitution, Croatia. Mile Skoric replaces Ivan Perisic.
Delay in match because of an injury Ivan Perisic (Croatia).
Marcelo Brozovic (Croatia) is shown the yellow card for a bad foul.
Foul by Marcelo Brozovic (Croatia).
Rabbi Matondo (Wales) wins a free kick in the defensive half.
Attempt saved. David Brooks (Wales) left footed shot from the centre of the box is saved in the bottom left corner. Assisted by Gareth Bale.
Attempt saved. Andrej Kramaric (Croatia) right footed shot from the centre of the box is saved in the centre of the goal. Assisted by Mario Pasalic with a through ball.
Attempt missed. Harry Wilson (Wales) header from a difficult angle on the right is high and wide to the right. Assisted by Gareth Bale with a cross.
Attempt missed. Andrej Kramaric (Croatia) right footed shot from the right side of the box is close, but misses to the right. Assisted by Luka Modric with a through ball.
Luka Modric (Croatia) wins a free kick in the attacking half.
Foul by Jamie Lawrence (Wales).
Borna Barisic (Croatia) wins a free kick in the defensive half.
Foul by Rabbi Matondo (Wales).
Attempt missed. Ivan Perisic (Croatia) left footed shot from the left side of the box is close, but misses to the left. Assisted by Andrej Kramaric.