Diamanti secures vital goal for Bologna
Diamanti scored the only goal of the game in the 54th minute to give Bologna its first win in five games and move the club two points above Cagliari and six away from the relegation zone.
The game took a while to get going, with nerves clearly showing in both sets of players. There would have been plenty more goals but for several brilliant stops by both goalkeepers.
Cagliari striker Joaquin Larrivey also hit the crossbar shortly after two good chances for Andrea Cossu and Thiago Ribeiro to equalize.
The visitors were lucky not to be reduced to 10 men in the first half following a poor challenge from Michele Canini.
Bologna could have taken the lead in the ninth minute when Robert Acquafresca unleashed a powerful shot from the corner of the area which Cagliari goalkeeper Michael Agazzi did well to stop.
Cagliari's first sight of goal came in the 18th as Cossu put in a brilliant cross to pick out Joaquin Larrivey one on one with Jean-Francois Gillet but the Argentine miscontrolled the ball.
The best chance of the first half fell to Bologna, shortly after the half hour, as Diamanti rushed onto Archimede Morleo's cross and fired through a crowd of bodies, but Agazzi parried well and then did even better when Acquafresca followed up.
Cagliari defender Canini might have been sent off five minutes from halftime when he brought down Acquafresca from behind as the Bologna striker was running clear through on goal.
Bologna felt further aggrieved four minutes after the break when Albin Ekdal pushed over Morleo as he crossed the ball. The defense cleared but only as far as Nico Pulzetti, who forced Agazzi into another brilliant save.
The home side called loudly for a penalty and, although it perhaps should have been a free kick on the edge of the area, the referee gave nothing.
Bologna almost found itself behind moments later but Gillet pulled off a great save to keep out a fierce effort from Daniele Conti.
The game sparked into life when Diamanti curled a stunning 30-yard free kick into the top right corner which Agazzi could do nothing about.
Cagliari had two golden opportunities to level. First, Agazzi's goal clearance bounced once before landing perfectly for Cossu, one on one with the goalkeeper, but his volley was brilliantly saved by Gillet.
Shortly afterwards, a mixup between Gillet and Nicolo Cherubin saw the latter clear straight to Thiago Ribeiro, who found himself alone in front of goal, but the Brazilian fired wide of the right upright.
Cagliari was almost made to rue those missed opportunities immediately as Acquafresca was set up perfectly by Gaston Ramirez but he miskicked and his effort scraped past the outside of the right hand post.
The visiting side again went even closer to the equalizer in the 70th when Larrivey headed Cossu's corner onto the crossbar.
Bologna coach Stefano Pioli was sent to the stands for dissent as tempers flared in the dying stages.