Lewandowski and Boateng's professionalism impresses Kovac
The duo had been expected to leave the Allianz Arena ahead of the new campaign, with Real Madrid reportedly interested in Lewandowski and Manchester United keen to take Boateng to Old Trafford.
Those moves failed to materialise, though, and both have been instrumental in Bayern's perfect start to the season under new boss Kovac.
Speaking at a media conference ahead of his side's Bundesliga match against Augsburg on Tuesday, Kovac said: "These are great professionals, world-class players. They know what they have to do.
"That they play so well does not surprise me. That's what I hoped for and expected."
James Rodriguez is another player who has started the season in fine form. The Colombian scored his second of the campaign in Saturday's 2-0 win over Schalke, but it was his work ethic that most impressed Kovac.
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"He's playing well," the former Eintracht Frankfurt boss added. "He always makes himself an option and comes up with a solution.
"He's working for the team and is gaining a real reputation for it, not just here in Munich but across the world."
Victory against Augsburg would make it five in a row in the league, but Kovac has warned his players not to get carried away.
"We are happy that we have started so strongly, but we can't become complacent," he said.
"We need to maintain our focus."