Testifying for the first time in the case, Suu Kyi appeared frail and pale but managed an occasional smile. A judge questioned her for less than half an hour about John W. Yettaw, who swam uninvited to her lakeside house.
The 63-year-old Nobel Peace laureate faces a possible prison term of up to five years in a trial that has brought worldwide outrage and led many countries in the West to say they are considering ramping up sanctions against the ruling junta. She is not expected to testify again, although she will continue to be present for the rest of the trial.
The charge against Suu Kyi is widely considered a pretext to keep her detained ahead of elections the military government has planned for next year. She pleaded not guilty Friday.
Myanmar's courts operate under the influence of the military and almost always deal harshly with political dissidents.
Suu Kyi's latest round of house arrest - extended every year since 2003 - was supposed to expire this week, and a top police official told diplomats Tuesday that the government had considered releasing her on "humanitarian grounds."
But the junta reversed that decision when the "unexpected incident of the intrusion of the American happened," Brig. Gen. Myint Thein said. The regime's critics, however, have assumed that the junta was looking for a pretext to keep her locked up.
She has spent more than 13 of the past 19 years in detention without trial, most at her dilapidated Yangon home.
Reporters and diplomats, including a reporter for The Associated Press, were allowed into the courtroom for Tuesday's session, the second time during the trial that such rare access has been granted.
"Thank you for your concern and support. It is always good to see people from the outside world," she told reporters and diplomats before being escorted out of the court by four policewomen.
Suu Kyi's side does not contest the facts of the case: She acknowledges that she allowed Yettaw, 53, to stay after he entered her house uninvited and then subsequently said he was too ill to leave immediately.
In testimony and a written statement to the court, she has also said she did not alert authorities to his presence because she feared getting him and the security personnel guarding her house in trouble, according to her lawyers.
Suu Kyi told the judge Tuesday that she did not immediately know when Yettaw - who was also in the courtroom - entered her house, but that at 5 a.m., one of her women companions informed her "that a man had arrived."
When asked if she reported his presence to the authorities, Suu Kyi said, "No, I did not." She said she spoke to Yettaw and gave him "temporary shelter," and he left just before midnight May 5.