Sergio Perez denied home hero Charles Leclerc a practice clean sweep as the two drivers look set to battle for pole position for the Monaco Grand Prix.
After finishing quickest in both sessions on Friday, albeit only 0.044s ahead of Ferrari team-mate Carlos Sainz at the end of FP2, Leclerc again looked set to hold sway in the final hour-long run.
But the Monégasque was pipped right at the death by Perez in his Red Bull, with the Mexican posting a time of one minute 12.476s to edge Leclerc who had been just 0.037s ahead in the dying moments.
Perez, though, is under investigation by the stewards for impeding Mercedes' George Russell at one stage during a lively session.
Leclerc had seemed to be the man to beat given his Friday performance but Red Bull has found extra pace overnight to give Perez a shot at pole with team-mate Max Verstappen seemingly not in contention at this stage.
Leclerc's team-mate Sainz finished third quickest, 0.370s down, with reigning champion Verstappen fourth on the timesheet, a further 0.035s back.
AlphaTauri's Pierre Gasly has looked strong so far this weekend and was best of the rest on this occasion, almost nearly eight-tenths of a second behind the leading duo.
The Frenchman was just 0.016s ahead of McLaren's Lando Norris who is set for a spot on the third row of the grid given his performances on this tight, twisty track so far.
Given the issues in practice on Friday with a stiff Mercedes and the level of bouncing across Monaco's bumpy streets, Lewis Hamilton managed to elevate himself up to seventh, but with the seven-time champion nine-tenths of a second down.
Haas driver Kevin Magnussen, Russell and Alpine's Fernando Alonso completed the top 10, followed by AlphaTauri's Yuki Tsunoda and the second Haas driver of Mick Schumacher.
The drivers from fifth to 12th were covered by just six-tenths of a second.
Alfa Romeo's Valtteri Bottas and McLaren's Daniel Ricciardo paid the price for their lack of running on Friday as the duo were down in 14th and 16th.
Bottas missed all of FP1 with a technical issue, while Ricciardo crashed early in FP2.
Williams' Nicholas Latifi again brought up the rear, nearly 2.5s adrift.
Monaco Grand Prix third practice results
1. Sergio Perez [Red Bull] 1:12.476
2. Charles Leclerc [Ferrari] +0.041s
3. Carlos Sainz [Ferrari] +0.370s
4. Max Verstappen [Red Bull] +0.405s
5. Pierre Gasly [AlphaTauri] +0.734s
6. Lando Norris [McLaren] +0.750s
7. Lewis Hamilton [Mercedes] +0.899s
8. Kevin Magnussen [Haas +0.960s
9. George Russell [Mercedes] +1.000s
10. Fernando Alonso [Alpine] +1.109s
11. Yuki Tsunoda [AlphaTauri] +1.169s
12. Mick Schumacher [Haas] +1.351s
13. Sebastian Vettel [Aston Martin] +1.362s
14. Valtteri Bottas [Alfa Romeo] +1.373s
15. Alexander Albon [Williams] +1.406s
16. Daniel Ricciardo [McLaren] +1.628s
17. Esteban Ocon [Alpine] +1.784s
18. Lance Stroll [Aston Martin] +2.163s
19. Zhou Guanyu [Alfa Romeo] +2.385s
20. Nicholas Latifi [Williams] +2.434s