text: Rosberg was 0.275 seconds quicker than Ferrari's Kimi Raikkonen, with the Red Bulls of Max Verstappen and Daniel Ricciardo close behind.
  Hamilton failed to complete a clean lap on his qualifying simulation on the ultra-soft tyres and ended up seventh.
  He finished his session early because of a recurring hydraulic problem.
  Hamilton was unable to do any of the race-simulation runs the teams do in the second part of the session on heavy fuel loads.
  He was also unhappy with the balance of the car on the ultra-soft tyre that was used for the fastest runs, although Mercedes believe they should be able to solve that problem with set-up changes.
  Hamilton, who is two points ahead of Rosberg in the world championship, is nevertheless heading into the weekend at a disadvantage.
  However, he can console himself with the knowledge that he had been fastest of all after the first runs in the session were complete, before he started to run into difficulties.
  "We had a small hydraulic issue at the end of FP2 but it doesn't look like anything serious," said Hamilton. "The guys are working on it and it should be fine for tomorrow, which is the main thing."
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  The evidence of the day was that Mercedes are not struggling in the same way as they did last year in Singapore, when their previously dominant car was more than a second off the pace of Ferrari and Red Bull.
  Listen again: A look ahead to the Singapore Grand Prix
  But, considering the long 3.15-mile lap, the margin between the world champions and their closest challengers is much smaller than normal.
  Verstappen was 0.380secs off Rosberg's pace, with Ricciardo just 0.025secs further adrift after recovering from a spin during which he brushed the wall without major damage.
  Verstappen was running a Renault engine upgrade which will not be available to Ricciardo until Saturday and which team boss Christian Horner said was expected to be worth in the region of 0.1secs a lap.
  And on race pace, Red Bull appeared to have an advantage but the picture was not completely clear.
  "We knew they wouldn't have a massive gap here this weekend," said Ricciardo. "We know if we get it right we can be very close in qualifying."
  Ferrari's Sebastian Vettel was fifth quickest after an unconvincing qualifying simulation run, 0.7secs slower than Raikkonen and a second slower than Rosberg.
  Vettel's problems put him back in the mix with the midfield runners, headed by Force India's Nico Hulkenberg in sixth.
  Toro Rosso's Carlos Sainz was eighth, ahead of Fernando Alonso's McLaren, a position with which the former champions are likely to be a little disappointed.
  They expected to be battling for seventh behind the big three, but Alonso was 0.6secs slower than Hulkenberg.
  The Spaniard's team-mate Jenson Button, meanwhile, was struggling - he was three places and a whopping 0.795secs behind Alonso, who is admittedly at his absolute best around the challenging Singapore track.
  Alonso had to park his car on track at the end of the session after encountering a gearbox problem.
  Englishman Jolyon Palmer was 17th fastest, just 0.005secs behind Renault team-mate Kevin Magnussen as both men fight for their future in F1.
  Singapore Grand Prix practice results
  Singapore Grand Prix coverage details
target: Nico Rosberg set the pace just ahead of Ferrari and Red Bull as Lewis Hamilton hit trouble in second practice at the Singapore Grand Prix.