André Villas-Boas has accused Danny Welbeck of cheating, as he reopened the wounds from last Sunday's 3-3 draw against Manchester United at Stamford Bridge and sought to highlight what he believes is a new phenomenon of attacking players buying penalties.

Chelsea were 3-1 up, having already conceded one penalty for Daniel Sturridge's foul on Patrice Evra, which was converted by Wayne Rooney, when Welbeck appeared to initiate the merest of contacts with Branislav Ivanovic, who had done everything he could to pull out of the challenge. The referee Howard Webb pointed to the spot, Rooney scored again and United's comeback was ignited.

Villas-Boas also pointed out a similar incident at Manchester City the previous day, when Adam Johnson had, in his words, "anticipated contact" with Fulham's Chris Baird to win a penalty.

"In the end," Villas-Boas said, "it is the player who proves his smartness – some are called cheats and divers, others are clever and smart for making the most of the situation, depending on your perspective. But the second one last week triggered United's comeback; at 3-2, they were right back in the game. I think Ivanovic made the right decision. He was inside the box. He was doing everything in his power to avoid contact and Welbeck sticks his leg out to find Ivanovic's leg, and the ref gives a penalty for that."

There was incredulity and no little sarcasm in Villas-Boas' tone. "Frustration is seeing a penalty like that given," he said. "There must be a new rule. We have them for two-footed tackles, now we have to have them for players who stick out their leg on purpose … clipping the leg of a defender on purpose to fall to give a penalty. On the same weekend, we had two incidents of that from Johnson and Welbeck. So there needs to be a new rule for penalties when the attacker purposely sticks his foot out to dive for a penalty. It is not a criticism of referees. It is a new rule.

"There is a consistency in this action now. Where the attacker on purpose leaves his leg out to be clipped when the defender is avoiding contact, then there must be a new rule set out for penalties to be given. It is not only fouls from a defender; now, the attacker has a right to get a penalty when they leave their foot out."

Villas-Boas has felt aggrieved about both of Chelsea's fixtures against United this season. After the 3-1 defeat at Old Trafford in September, he made an official complaint to Mike Riley, the head of the Premier League match officials, arguing that United's first two goals ought to have been disallowed for offside. He appeared to have some sympathy for the difficult job of the officials but he feels that standards must improve.

"Referees have clear orders on simulation but it is difficult for them to assess the difference between simulation and fouls," Villas-Boas said. "I'm sure the referees are adapting and hopefully, you will see better performances from them. But it is up to Mike Riley and the governing bodies to decide if the refereeing is up to the right level and to punish the ref.

"My view on our last game is that, if the referee is going to award two penalties away from home to the same team, he should be 100% sure they are both penalties. Howard Webb was obviously 100% sure in his own mind. My opinion is different, that he was wrong. End of story. But for the same team to get two penalties in a game is not very usual and for that to happen to the same team twice in the same week is very unusual."