Arsenal held Chelsea to a goalless draw in the first leg of their Carabao Cup semi-final on Wednesday night.
It was the Video Assistant Referee (VAR) system that took centre stage during a relatively uneventful affair at Stamford Bridge, as referee Martin Atkinson used the technology twice to assess two penalty shouts in either half, neither of which were given.
Chelsea had the better of the chances on the night, but could not break through Arsenal to leave the tie wide open heading into the second leg at the Emirates in two weeks.
Chelsea fielded a strong side with Eden Hazard, Alvaro Morata and Cesc Fabregas all starting, alongside Danny Drinkwater.
David Ospina started in goal for Arsenal, while Alex Iwobi, Danny Welbeck and Alexandre Lacazette also all played. Alexis Sanchez was on the bench and Mesut Ozil was injured.
For the second time, after Brighton and Crystal Palace met in the FA Cup on Monday night, the VAR system was being used in English football, and Atkinson wanted clarification on his decision not to award a penalty for a Victor Moses challenge on Ainsley Maitland-Niles in the 39th minute, which proved correct.
Chelsea did then come close to an opener on the stroke of half-time as a trademark deep cross from Cesar Azpilicueta found Cesc Fabregas in the box, but he could only head straight at David Ospina from an unmarked position.
The Blues came close again just after the break as they threatened from a short corner, but Andreas Christensen could only nod over from close range after Marcos Alonso had flicked a cross into his path.
Arsenal then suffered a blow just before the hour-mark when they lost Jack Wilshere, who was captain, to injury. It was an all-too familiar sight as the midfielder appeared to land awkwardly and hurt his ankle, before being replaced by Mohamed Elneny.
Chelsea: Courtois (6), Azpilicueta (7), Christensen (7), Rudiger (7), Moses (6), Kante (6), Fabregas (7), Drinkwater (6), Alonso (6), Hazard (7), Morata (6)
Subs: Bakayoko (n/a), Willian (n/a), Batshuayi (n/a)
Arsenal: Ospina (7), Bellerin (6), Chambers (7), Mustafi (7), Holding (7), Maitland-Niles (5), Wilshere (7), Xhaka (6), Iwobi (5), Welbeck (6), Lacazette (5)
Subs: Elneny (n/a), Sanchez (n/a)
Man of the match: Calum Chambers
Arsene Wenger, who was serving the second match of his touchline ban from the Stamford Bridge press box, then threw Alexis Sanchez on for Alexandre Lacazette, with the substitution being jeered by a section of the away end.
There was some more use of the VAR late on as Danny Welbeck appeared to trip Fabregas in the box, but once again referee Atkinson's initial decision was justified by the video replays.
- Chelsea have now failed to score in just three home games in all competitions under Antonio Conte - all of them have been this season and two have been against Arsenal.
- Indeed, Arsenal are only the second team ever to keep two clean sheets away at Chelsea in the same season, after Manchester United in 1998-99.
- The Blues have had consecutive goalless draws in all competitions for the first time since November 2012.
- All four meetings between these sides in all competitions this season have ended level - the last time two Premier League teams drew four games against each other in the same season was Blackburn vs Sunderland in 2002-03.
- Chelsea have progressed on each of the three occasions they've drawn the first leg of a League Cup semi-final - vs Man Utd in 2005, Wycombe in 2007 and Liverpool in 2015.
- Meanwhile, Arsenal have progressed just once from the three previous occasions they've drawn the first leg - going through against Tottenham in 2007, but failing against Aston Villa in 1996 and Tottenham in 2008.
Man of the match - Calum Chambers
It wasn't a vintage Carabao Cup semi-final and chances were few and far between, but Calum Chambers put in an assured display as part of Arsenal's defence in repelling Chelsea's attack.
Antonio Conte: "For me, there's disappointment about [not enough] extra time. In the second half, the doctor went onto the pitch twice and the referee stopped for VAR, so you have to give more minutes of extra time. In Italy sometimes extra time can be seven, eight or nine minutes.
"There's a bit of disappointment because it's important to try and win every game. We tried to use our strengths to win it and we created chances to score, but we were not clinical enough."
Arsene Wenger: "I felt there was a great togetherness and discipline in the team. We didn't give many chances away and I'm pleased with the spirit and determination we've shown.
"We wanted to be solid defensively but of course to score as well. We were close a few times but overall I think the team responded very well."
Both sides are back in Premier League action this weekend. Chelsea host Leicester on Saturday 3pm, while Arsenal travel to Bournemouth on Sunday in the first part of Super Sunday on Sky Sports, with kick-off at 1.30pm