The two-time world champion completed the Valencia Street Circuit in 1:39.283 in the second practice session as times tumbled from those set in the early morning session.
Alonso found almost three seconds between his best time in practice one, and his fastest lap in practice two as the circuit rubbered in, while McLarenÃ¢â‚¬â„¢s Lewis Hamilton found just 2.5 seconds in the second session.
Red BullÃ¢â‚¬â„¢s Sebastian Vettel and Mark Webber recovered from disappointing first sessions to finish second and third within two tenths of Alonso, while the McLarens of Hamilton and Jenson Button could only finish fifth and ninth despite finishing second and third during first practice.
The top 10 were separated by just one secondÃ¢â‚¬â€perhaps an indication that tomorrowÃ¢â‚¬â„¢s qualifying could be the closest yet this season.
Despite snooze-fests in 2008 and 2009, Valencia is seen as the one to watch with several teams bringing their own version of Red BullÃ¢â‚¬â„¢s blown diffuser, said to be worth up to 0.5 seconds per lap.
Ferrari and Mercedes are particularly keen to harness any advantage they can get to closing in, while championship leaders McLaren will save their upgrade for Silverstone when the blown diffuser will be even more effective.
It is telling that both Mercedes and Ferrari topped the time sheets on Friday following in their upgraded cars as Nico Rosberg took the first session ahead of the McLarens.
McLaren, Red Bull, Mercedes and Ferrari are all evenly-matched ahead of SaturdayÃ¢â‚¬â„¢s final free practice session leaving many questions over who could take pole.
At the back there were few surprises as Lotus outpaced rivals Virgin and Hispania.
Heikki Kovalainen was fastest of the new teams with a time of 1:42.467, despite only arriving at the circuit this morning after having to drive down to Valencia from Geneva with his physio Petri due to being caught up in another French air strike.
Teammate Jarno Trulli was half a second back with a time of 1:42.993.
The super soft compound caused problems with most drivers, as the faster times came on the prime medium compound despite track temperature appearing to be stable at 44 degrees.
SaturdayÃ¢â‚¬â„¢s practice session is 10am BST ahead of qualifying at 13:00 BST
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BIOGRAPHY: Lucas Torreira