Chelsea extend unbeaten run to 20 games but fail to break down gritty Sunderland John Terry and Chelsea endured a frustrating night at the Stadium Of Light. PREMIER League leaders Chelsea had to be content with a point as they were held to a 0-0 draw at battling Sunderland. Jose Mourinho's side increased their advantage at the top of the table to seven points thanks to a 13th league game without defeat, stretching their unbeaten start to the season to 20 games in the process. But they left the Stadium of Light frustrated at being unable to press home their territorial advantage against the hardworking hosts, who drew for the eighth time this campaign. Diego Costa came in for some close attention. Gus Poyet's side remain the last team to beat Chelsea in the Premier League, a 2-1 victory at Stamford Bridge more than seven months ago. It proved an eventful evening for Diego Costa, the Blues" star striker, who was lucky not to be sent off as the Spaniard earned a second-half caution after being fortunate to escape a yellow card at the end of the first-half. Mourinho wisely substituted his 12-goal top scorer, who will be suspended for this week's Premier League visit by Tottenham after his fifth booking of the campaign. Despite enjoying the lion's share of the ball for the entire contest, the unchanged visitors were made to work hard by Poyet's side, who hit the bar just before the break as Santiago Vergini latched onto Lee Cattermole's pass to send a first-time effort against the woodwork from close range. An at-times tetchy contest all got too much for Mauricio Taricco and as half-time approached, the Sunderland coach was banished from the dugout to the stands by referee Kevin Friend for his overly-robust sideline protests as the Black Cats were denied three free-kicks in quick succession. Sunderland goalkeeper Costel Pantilimon was pretty happy with the point. Despite chasing shadows for much of the first-half, Sunderland stuck to their task. Strikers Steven Fletcher and Connor Wickham both went close with half-chances, before recalled midfielder Jack Rodwell, Sunderland's only change, tried his luck from distance. Thibaut Courtois, the Chelsea goalkeeper, was easily up to the task. As half-time approached, Costa inexplicably escaped censure, when the striker kicked out at John O'Shea after going to ground in a tussle with the Sunderland skipper, the Spaniard grateful for Friend's leniency after an ugly studs-up lunge at the Irishman. The interval failed to halt Chelsea's momentum, and Gary Cahill should have put them ahead straight after the restart, but the England defender headed Willian's pinpoint corner straight at Pantilimon from six yards under pressure from O'Shea and Wes Brown. Willian was then inches away from grabbing a spectacular opener when the Brazilian jinked his way past Anthony Reveillere to fire just wide. Costa finally made his way into Friend's book, when his trailing arm accidentally caught Brown in the face to earn a fifth caution of the season, his last notable contribution before being withdrawn. Pantilimon held a Nemanja Matic long-range effort at the second attempt in a scare for Sunderland. However, the hosts remained a threat on the counter-attack, and Courtois had to be alert to hold onto a snap-shot from Wickham as the forward tried his luck form the edge of the area. Originally published as Chelsea kept in check by gritty Sunderland