Daniel Ricciardo (Red Bull) topped the final practice session to make it a hat-trick of free practice sessions in first, ahead of team-mate Max Verstappen who crashed in the dying minutes.
In the early stages of the session, the Ferrari drivers traded places at the top of the timesheets with Kimi Raikkonen setting an early benchmark of 1:13.033.
The Toro Rosso’s demonstrated respectable lap times early on, with Brendon Hartley and Pierre Gasly both entering the top five.
The Red Bulls then shattered the morale as Verstappen managed to post the fastest time of the weekend with a 1:11.787.
However, as the session reached its conclusion, the red flag was deployed after Verstappen clipped the inside barrier at the Swimming Pool chicane, breaking the suspension and causing him to crash.
The incident mirrored that of the one he had in 2016, and now his mechanics are currently in a race against time to repair the car for qualifying.
The session was restarted with three minutes left and Ricciardo managed to pip the Dutchman by one thousandth of a second to end the session on top.
— Tim Hauraney (@timhauraney) May 26, 2018
Valtteri Bottas (Mercedes) languished in 12th with 20 minutes left, caused in part by a trip down the escape road at St Devote.
The flying Finn – whose helmet this weekend pays tribute to fellow countryman and double World Champion Mika Hӓkkinen – managed to go up to sixth towards the end, albeit half a second off the pace.
In the sister car, Lewis Hamilton also found it difficult to extract pace out of the Silver Arrows as he finished fifth.
Hartley’s lap from the beginning of the session was good enough for seventh, with Gasly close behind in eighth.
Sergey Sirotkin (Williams) put in an impressive display his in first weekend at the principality to slot in ninth place.
In contrasting fortunes, Lance Stroll didn’t produce this level of pace as he experienced understeer and finished 16th.
Carlos Sainz Jr. (Renault) had an issue with his steering going to the left as he completed the top ten.
Further down the order, Haas struggled for pace due to issues with their tyre temperatures.
Romain Grosjean experienced further frustration as he came across traffic during his runs, including being held up by his team-mate Kevin Magnussen.
|Pos.||Car No. Driver (Nationality), Team||Time (Laps)|
|1||3 Daniel Ricciardo (AUS), Red Bull Racing||1:11.786 (23)|
|2||33 Max Verstappen (NLD), Red Bull Racing||1:11.787 (14)|
|3||5 Sebastian Vettel (DEU), Scuderia Ferrari||1:12.023 (23)|
|4||7 Kimi Rӓikkӧnen (FIN), Scuderia Ferrari||1:12.142 (26)|
|5||44 Lewis Hamilton (GBR), Mercedes AMG||1:12.273 (26)|
|6||77 Valtteri Bottas (FIN), Mercedes AMG||1:12.356 (27)|
|7||28 Brendon Hartley (NZL), Scuderia Toro Rosso||1:12.752 (25)|
|8||10 Pierre Gasly (FRA), Scuderia Toro Rosso||1:12.761 (23)|
|9||55 Carlos Sainz Jr. (ESP), Renault||1:12.850 (24)|
|10||35 Sergey Sirotkin (RUS), Williams||1:12.854 (23)|
|11||2 Stoffel Vandoorne (BEL), McLaren||1:12.874 (25)|
|12||31 Esteban Ocon (FRA), Force India||1:12.940 (23)|
|13||11 Sergio Perez (MEX), Force India||1:13.025 (22)|
|14||27 Nico Hulkenberg (DEU), Renault||1:13.112 (26)|
|15||14 Fernando Alonso (ESP), McLaren||1:13.279 (25)|
|16||18 Lance Stroll (CDN), Williams||1:13.595 (26)|
|17||16 Charles Leclerc (MON), Sauber||1:13.644 (25)|
|18||8 Romain Grosjean (FRA), Haas||1:13.881 (21)|
|19||20 Kevin Magnussen (DEN), Haas||1:14.192 (20)|
|20||9 Marcus Ericsson (SWE), Sauber||1:14.221 (28)|