* Hamilton fastest in both sessions
* Mercedes drivers ahead of the rest (Adds quotes, protest march elsewhere)
By Alan Baldwin
MANAMA, April 4 (Reuters) - Lewis Hamilton led Mercedes team mate Nico Rosberg in a shimmering one-two in floodlit practice for the Bahrain Grand Prix on Friday.
The 2008 world champion, winner in steamy Malaysia last weekend ahead of championship leader Rosberg, picked up where he left off on the first day of action at the Sakhir desert circuit.
Hamilton was fastest in both sessions with a best time of one minute 34.325 seconds in cooler evening conditions after a 1:37.502 in the afternoon sunshine.
Sunday's race, the 10th held in the restive Gulf kingdom since Bahrain hosted the Middle East's first Formula One grand prix, has moved to a day-to-night format.
With the cars gleaming in the glare of 5,000 bulbs illuminating the track from the newly-installed floodlights, the sleek 'Silver Arrows' stood out as expected pacesetters.
Rosberg's fastest lap, in a session that saw track temperatures drop from 33 degrees Celsius on a bright and breezy afternoon to a balmy 25 after dark, was 0.365 slower than his British team mate.
"It's been a pretty decent day. I've loved driving today, and the car feels better here now than it did when we were here testing, and I've a much better feel of where I need to put the car so I'm very happy with the practice sessions," said Hamilton.
"But it's still going to be tough, particularly with the temperatures dropping all the time, so the balance is shifting throughout the run. So it's still going to be a real challenge."
Hamilton, used to racing at night in Singapore and Abu Dhabi, said visibility had been perfect and he had hardly noted a difference.
SENSOR FAILURE
Ferrari's Fernando Alonso was third fastest in both sessions, with Red Bull's Daniel Ricciardo fourth in the evening and Force India's Nico Hulkenberg filling that spot in the afternoon.
Ricciardo again suffered problems with his car's fuel flow sensor, the same part that has failed in both of the first two races of the season.
Alonso's team mate Kimi Raikkonen meanwhile damaged the floor of his car when he hit a kerb, a fate that also befell Lotus's Pastor Maldonado.
McLaren's Jenson Button, the 2009 world champion who will be starting his 250th race on Sunday, was fifth and sixth in the respective sessions.
The timesheets reinforced Mercedes' early-season superiority, with four cars powered by their engines in the top five after lunch.
Williams, who also have Mercedes engines, had Brazilian Felipe Massa fifth in the evening session despite sitting out the first half of the session because they already had plenty of data from eight days of pre-season testing in Bahrain.
Red Bull's quadruple world champion Sebastian Vettel was 10th and seventh.
Alonso provided some surprise when Ferrari accidentally sent him out with one soft tyre and three mediums on his car in the first session. The Spaniard stopped in the pit lane and was pushed back.
Three reserve drivers made debut appearances for the season in first practice, with Brazilian Felipe Nasr given track time at Williams, Dutchman Giedo van der Garde at Sauber and compatriot Robin Frijns at Caterham.
The sessions were untroubled by protests elsewhere against the race, the country's biggest annual sporting event which the government sees as a major boost for Bahrain's international profile as well as attracting tourists and investment.
Bahrain has suffered sporadic unrest since an uprising led by its Shi'ite Muslim community in early 2011 demanding reforms and a bigger share of power in the Sunni-led government.
An estimated 20,000 mainly Shi'ite protesters marched in northwestern Bahrain to demand reforms and release of prisoners.
Police kept a distance from the march, which moved along 3.5km on a highway west of Manama and ended peacefully. (Reporting by Alan Baldwin, editing by Julien Pretot and Toby Davis)
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